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EFFECTS OF MARIJUANA ON OTHER BIOLOGICAL SYSTEMS This chapter covers what little is known about the effects of cannabis on male and female reproduction and endocrine systems, birth defects and teratogenic effects, genetics, the immune system, and body temperature. MALE REPRODUCTIVE FUNCTION A variety of studies indicate that marijuana and some of its derivatives have reversible, suppressive effects upon testicular function in animals and men. These have been measured in terms of diminished weights of the prostate gland, seminal vesicles, or testes, and in decreased levels of testosterone (the male hormone) in blood plasma or suppression of spermatogenesis following chronic or acute administration of cannabis or A-9-THC. Appropriate observa- tions have indicated that the effects of cannabinoids on the male reproductive tract and on testicular function were completely reversed l month after drug withdrawal. There is no general agreement as to the cause or magnitude of these effects. The major reasons for this lack of agreement relate to major differences in study design, including species studied (man, monkey, or rodent), route of drug administration, and purity of the drug used. Human Studies In l974, a group of 20 men were studied who had used marijuana at least 4 days a week for a minimum of 6 months without the use of other drugs (Kolodny et al., l974). Plasma testosterone levels in subjects smoking five to nine marijuana cigarettes per week were significantly lower than controls (however, only 2 had levels out of the normal range, i.e., below 400 ng/dl); all but l of the men smoking more than l0 marijuana cigarettes per week had testosterone levels below 400 ng/dl. These results suggest that there was a dose-dependent effect of marijuana on testosterone levels. Plasma levels of lutenizing hormone (LH) and follicle-stimulating hormone 94
95 (FSH), gonadotropins that control the growth of the ovaries or testes and their hormonal activities, were in the normal range; however, in men smoking more than l0 marijuana cigarettes per week, the FSH level was significantly lower than for those who smoked 5 to l0 marijuana cigarettes per week. Because only random samples of blood were obtained for gonadotropic measurements, small but significant changes could have been missed. Levels of prolactin, the female hormone involved in lactation and also present in small quantities in men, were all in the low normal range. In addition, the men who smoked more than l0 marijuana cigarettes per week had significantly lower sperm counts than those who smoked the lesser quantity (26 versus 68 million/ml). These individuals obtained marijuana from a variety of sources, and there was no way to determine whether they were taking other drugs that could lower plasma testosterone. Later in l974, another study reported that plasma testosterone levels were not suppressed in 27 men studied in a research ward (Mendelson et al., l974) These individuals smoked marijuana cigarettes supplied by the federal government. For unexplained reasons, the mean testosterone levels in these individuals were greater than l,000 ng/dl (higher than the normal mean) before and during the smoking periods. This is in marked contrast to the mean value of 742 ng/dl for nonsmokers in the study of Kolodny et al. mentioned above. There was no report of gonadotropic values or semen analysis in the Mendelson Study. A study of l6 patients on a metabolic ward who smoked NIDA cigarettes (Hembree et al., l979) showed that 5 to 6 weeks of high-dose (2 percent) marijuana administration (8-20 cigarettes/day) was associated with a decline in sperm count during the fifth and sixth weeks after initiation of drug exposure. This was preceded by a decrease in sperm motility and an increase in abnormal forms of sperm. Once a week during the study five blood samples were obtained at l5-minute intervals for measurement of testosterone, LH, and FSH. No change in these hormone levels was noted throughout the study (although no values were reported). The relationship in time of these samples to the last previous cigarette was not mentioned, therefore the test would not have excluded a transient decline in hormonal levels after each cigarette. However, because hormonal suppression of spermatogenesis takes longer than 4 weeks and usually is not associated with an increase in the number of abnormal forms and a decrease in motility, the authors concluded that the effect upon the seminiferous tubular epithelium was direct rather than by suppression of gonadotropins. This is the only reported study in man that measured the hour-to-hour fluctuations in gonadotropic levels. Another study (Coggins et al., l976) evaluated the health status of 84 marijuana smokers who had used the agent three or more times per week for a minimum of l0 years. Testosterone levels were measured in 38 users and 38 nonusers. The mean levels and ranges were virtually identical. This heterogeneous group of men patients studied in Costa Rica was not recruited for the purpose of studying the pituitary-gonadal axis. No gonadotropic levels or semen samples were studied.
96 Endocrine function studies are briefly mentioned in a paper by Cohen (l976). Subjects were recruited on the basis of heavy marijuana use and were studied in a metabolic ward. They smoked an average of five marijuana cigarettes per day, which was believed to be the equivalent of l03 mg of A-9-THC. During acute administration, mean levels of plasma testosterone declined from 754 to 533 ng/dl over a 3-hour period. After 9 weeks of smoking, plasma testosterone levels had declined from 740 to 509 ng. Plasma LH levels were reported to have fallen after the fourth week; however, no absolute values were given. In addition, no standard errors are given for any of the means presented in this paper. Therefore, it is impossible to evaluate the significance of the reported findings. In Greece, a population of 47 chronic hashish users was studied. Electron microscope studies of the acrosome, the head of the sperm, showed abnormality in some patients (Issidorides, l979). It is difficult to evaluate the study because no quantitative data were presented. Animal Studies All of the studies mentioned below are substantially different from those of human beings because, with one exception, the active agent (usually A-9-THC) was administered intraperitoneally at a dose of 2.5 to 25 mg/kg. Based on calculations given by Cohen (l976), 3 to 6 mg/kg/day would be considered a large dose in human beings.* Also, human beings self-administer the drug over many hours rather than as a single dose. In castrated rhesus monkeys, plasma LH and FSH fell acutely following acute administration of A-9-THC (Smith et al., l980). During this suppression period, both gonadotropins could be stimulated by lutenizing hormone-releasing factor (LHRF), which causes the release of LH. The effect of A-9-THC was to suppress prolactin release, which, in turn, could be stimulated by thyrotropin-releasing hormone (TRH). Studies in other species have tended to confirm these observations in monkeys. The results are compatible with the hypothesis that the effect of marijuana and its derivatives is on gonadotropic secretion (Harclerode et al., l979). Testicular cytochrome P-450 (an enzyme) decreased in the rat following 2 to 9 weeks of treatment. The concentrations of this enzyme, plus a variety of other testicular markers, were restored with FSH and LH therapy. The effect of various cannabinoids has been studied on sperm morphology in the mouse (Zimmerman et al., l979). *Rosenkrantz (l98l) considers 0.6-3.0 mg/kg by inhalation and l.8-9.0 mg/kg orally to be large doses in human beings. For the monkey, l.8-9.0 mg/kg by inhalation and 5-27 mg/kg orally would be considered a high dose. (These concentrations are equivalent to six c igarettes/day.)
97 Mice were given five daily intraperitoneal injections of A-9-THC, cannabidiol, or cannabinol at doses approaching or exceeding the LD5Q (the dose necessary to kill 50 percent of the animals). Thirty-five days after the last treatment, animals were killed and sperm were evaluated by scanning electron microscopy. Control animals had l.5 percent abnormal forms. Animals that received LD5o doses of the various derivatives had 2.4 to 5.0 percent abnormal forms. Only a few studies have examined the effects of cannabis on spermatogenesis (Huang et al., l979). Marijuana was administered to rats in a smoke machine. After 30 days of exposure, marijuana smoke lowered the sperm counts in animals significantly, as did cannabinoid-free smoke. By 75 days, however, only the marijuana smoke group maintained a low sperm count. In the marijuana-treated group, there was an increased number of abnormal forms, particularly with an increase in dissociation of sperm heads and tails. In the discussion of this paper, the authors reported elevated serum FSH levels following marijuana exposure, but did not present data. They concluded that marijuana has a direct effect on the testis. A variety of in vitro studies support this suggestion (Jakubovic et al., l977, l979). Marijuana and its derivatives also have been shown to be antiandrogenic (antagonistic to male hormones) (Purohit et al., l980). Several constituents, including A-9-THC, can bind to the receptor for androgen. Marijuana also has been demonstrated to be estrogenic (like female sex hormones) in vivo, and recent studies suggest that these effects may be mediated via the estrogen receptor. These observations have been disputed by others (reviewed by Purohit et al., l980). The ability to inhibit or mimic the action of sex steroids provides one mechanism by which these agents can produce their effects. There obviously are many others. FEMALE REPRODUCTIVE FUNCTION The effect of cannabis on female reproduction has been studied in rats, mice, rabbits, and monkeys. The work in rhesus monkeys is of particular importance, because of the similarity in the menstrual cycle among primate species, including human beings. Human Studies There is only one study reported on the effects of marijuana on reproductive function in women. The work has appeared in print as a report of the proceedings of a l978 symposium held in Mexico City (Bauman et al., l979) and as part of the congressional record subsequent to testimony before a Senate committee hearing (Bauman, l980). These publications do not provide details on methodology or on individual hormone values. Differences between the control and experimental groups, recognized by the investigators, could be of
98 importance; alcohol use, for example, was more frequent in the marijuana-using group. The study attempted to establish the endocrine (hormonal) profile and menstrual patterns of women who used marijuana on a chronic and frequent basis. Twenty-six women who used it at least three times a week for 6 months were compared with l7 women who had never used the substance. The number of cycles studied for each variable investigated is not clear from the publications. This difficulty notwithstanding, the report reveals no difference in plasma levels of LH and FSH between the two groups and no change in peaks and basal values of the female hormones estradiol or progesterone, the critical hormone levels controlling the process of ovulation. It would be expected that no major difference was found in the incidence of anovulatory cycles between the two groups. By combining anovula- tion and shortened luteal phase, however, the authors report a statistically significant difference in the marijuana-using group, which could be clinically important in causing subfertility. This evidence is, at best, only suggestive. The observation that testosterone levels in marijuana-using women are elevated is difficult to interpret in terms of clinical significance; apparently, the subjects did not report episodes of acne, abnormal hairiness, or other testosterone-dependent side-effects. According to the authors, serum prolactin levels are lower in marijuana users than in controls. The implications of this observation for fertility, lactation, or the development of breast cancer are not clear. The absence of other studies on users of marijuana makes it difficult to draw conclusions on the implications of the data cited above. Several of the effects noted are different from the more extensive and experimentally controlled observations in rhesus monkeys and other laboratory animals. This situation calls attention to the urgent need for more comprehensive endocrine and gynecologic investigations of women who use marijuana. Animal Studies Administration of crude marijuana extract to rats or mice resulted generally in suppression of ovarian function and in various aspects of estrogen activity, such as uterine metabolism, weight, glycogen content, and levels of RNA and sialic acid (Chakravarty et al., l975; Dixit et al., l975). The administration of crude marijuana extract for 30 days to rats and mice abolished the estrus cycle and caused a significant reduction in the size of the ovaries and in some primordial ova (Dixit et al., l975). Intraperitoneal administration of A-9-THC to rats, appropriately timed, has also been reported to block ovulation (Nir et al., l973). This effect of A-9-THC was exerted by suppressing the characteristic preovulatory surge of plasma LH. Other investigators have reported suppression also of plasma FSH and prolactin when A-9-THC is given just before ovulation (Ayalon et al., l977). The substance was found to depress plasma concentration of LH in ovariectomized rats (Marks, l973; Tyrey, l978, l980) and
99 rhesus monkeys (Besch et al., l977). Asch et al. (l979) also showed in the rabbit, a reflex ovulator, that a precoital single dose of &-9-THC blocks the postcoital LH surge and ovulation. Administration of LHRF was able to bring about the release of LH in A-9-THC treated rats and rhesus monkeys (Smith et al., l979). These results indicate a direct effect of cannabinoids at the level of the hypothalamus, part of brain important in reproductive hormone regulation. The ovulation-blocking effect of the cannabinoids was further investigated by Cordova et al. (l980). Natural and chemically modified cannabinoids blocked ovulation in rats. Administration of A-9-THC to rhesus monkeys during the follicu- lar phase resulted in prolonged periods of amennorhea (absence or abnormal stoppage of the menstrual flow), absence of midcycle LH surge, and progesterone levels characteristic of anovulation (Asch et al., l98l). BIRTH DEFECTS AND TERATOGENICITY Because A-9-THC crosses the placenta it is a potential teratogen, an agent that causes defects in the developing embryo. This effect could occur in either of two ways: (l) exposure to cannabis prior to conception could harm the sex cells (the ova and sperm), or (2) the fetus could be harmed directly during organogenesis. In addition, A-9-THC can be secreted in breast milk and, therefore, can be toxic postnatally. Human Studies The evidence for teratogenicity in human beings is very difficult to interpret. Although there is widespread use of marijuana in young women of reproductive age, there is no evidence yet of any teratogenic effects of high frequency or consistent association with the drug. There are isolated reports of congenital anomalies in the offspring of marijuana users, but there is no evidence that they occurred more often in users than in nonusers and in those cases there was coincident use of other drugs. Subtle development effects in offspring, such as nervous system abnormalities, and reductions in birth weight and height may indeed exist (Finnegan, l980; Fried, l980; Hingson et al., in press). Additional carefully designed, prospective studies should provide valuable information in this area. Animal Studies Crude marijuana extract and A-9-THC are teratogenic at certain doses in animals.* *Bibliography available upon request from the Institute of Medicine, National Academy of Sciences.
l00 One study reported that subcutaneous injection of pregnant hamsters and rabbits with various doses of crude marijuana extract caused malformations of the brain, spinal cord, forelimb, and liver, as well as edema of the head and spinal region in developing embryos (Gerber and Schramm, l969) . In hamsters, significant embryocidal and growth retardation effects also were noted. It was concluded that doses greater than 200 mg/kg in hamsters and 250 mg/kg in rabbits were teratogenic. Caution in interpreting these findings must be exercised because the teratogenic effects may be caused by any combination of constituents of the cannabis extract. In a study of mice, the teratological effects of A-9-THC were evaluated for doses ranging from 3.0 to 400 mg/kg by various routes of administrationâintravenous, subcutaneous, and intragastric (Joneja, l976). Significant fetal growth retardation was induced at higher dose levels and by some routes of administration. For example, a high dose of 400 mg/kg was significantly teratogenic by the intragastric route; l2.l percent of the live fetuses were malformed. In a study of female monkeys given an oral dose of 2.4 mg/kg A-9-THC for l to 4 years, a nonspecific pattern of reproductive difficulties was observed characteristic of "high-risk" pregnancies, including a high rate of offspring loss during pregnancy or in the early postnatal period (Sassenrath et al., l979). GENETIC EFFECTS The potential genetic effects of marijuana are of major concern because of its prevalent use by young people in their reproductive years (see Chapter 2). Although there is a growing amount of evidence that drugs can induce mutations, and an improving ability to use toxicological methods to evaluate agents for their mutagenic potential (such as the Ames test, which detects changes or damages in the genetic material), the available information on the genetic hazards or even on the potential genetic hazards of the use of marijuana is extremely limited. Mutagenicity Elsewhere in this report (Chapter 3) the scientific evidence that marijuana smoke and tar are mutagenic has been discussed. Lung explants of mice and human fibroblast cultures exposed to fresh smoke showed abnormalities of cell division, as well as changes in chromosome structure and in DNA synthesis (Leuchtenberger and Leuchtenberger, l97l; Leuchtenberger, et al., l973a,b). Moreover, extracts and smoke condensates of marijuana are mutagenic when evaluated by the Ames test (Busch et al., l979; Seid and Wei, l979; Wehner et al., l980). Animal studies on rodents painted with marijuana tar, three times weekly for l year, resulted in skin papillomas, carcinomas, and fibrosarcomas (Hoffmann et al., l975).
l0l However, extensive testing with A-9-THC using three established tests for mutagenesis failed to detect any mutagenic effect, or any effect as an inhibitor of DNA repair (Legator et al., l976; Glatt et al., l979; Zimmerman et al., l978). Cytogenetic Effects The numbers and kinds of chromosomes (structures in a cell nucleus that contain and transmit genetic information carried in DNA) are highly characteristic for a given species. Structural variation and changes in numbers of chromosomes may be evidence for genetic damage produced by drugs and other chemical agents. Unfortunately, the literature on the effects of marijuana on chromosomes is limited and conflicting. Studies suggesting that marijuana probably does not break chromosomes are fairly conclusive. There is less evidence that marijuana may produce aneuploidy (abnormal numbers of chromosomes) in some daughter cells during cell division. Does marijuana cause chromosome breaks? The weight of the evidence from in vitro cultures of human cells and from in vivo animal and human studies is that neither marijuana nor A-9-THC causes chromosome breaks. In Vitro and Animal Studies Cultures of human leukocytes, exposed to different concentrations of A-9-THC, showed no increase in the incidence of chromosome breaks or gaps when compared to controls (Stenchever and Allen, l972). Studies of golden hamsters given subcutaneous injections for l0 days of marijuana extract distillate containing l7.l percent A-9-THC (Nicholson et al., l973), and of beagle dogs trained to smoke high doses of marijuana (3 g/day/week for 30 months), showed no significant differences in chromosome gaps or breaks when compared with control groups (Genest et al., l976). Human Studies Cytogenetic analysis of chromosomes from peripheral blood leukocytes and cultures of subjects exposed to marijuana smoking, marijuana extract, or synthetic A-9-THC revealed no increase in chromosome breakage attributable to these compounds (Nichols et al., l974; Matsuyama, l976; Morishima et al., l979). Doses ranged from 20 mg A-9-THC per day to l2-l6 marijuana cigarettes per day. Studies that have reported chromosome breaks or gaps in cell cultures of users of marijuana have largely been carried out on multiple drug users, and the breaks and gaps may be due to other factors associated with a life of heavy drug use (Gilmour et al., l97l; Herha and Obe, l974). However, in a retrospective study on college students, chromosome breaks were found in blood cultures of 49 light (one or
l02 less exposure per week) and heavy (more than two exposures per week) users of marijuana (Stenchever et al., l974). One problem in this study is the poor dose characterization. Furthermore, the increase in the numbers of breaks in both light and heavy users of marijuana was not dose-related; the same frequency of breaks was observed in both groups. Although the evidence is inconclusive, it suggests that marijuana does not cause chromosome breaks. Does marijuana interfere with cell division and chromosome segregation, thereby resulting in abnormal numbers of chromosomes? There is conflicting evidence in the literature. On the one hand, no significant effects of marijuana smoke or A-9-THC on chromosome complement have been reported using the micronuclei test in mice or in cytogenetic studies in dogs (Genest et al., l976; Legator et al., l976). On the other hand, more extensive studies have demonstrated aneuploidy resulting from in vitro exposure of cells to marijuana as well as in vivo studies of animals and human beings. In Vitro and Animal Studies Exposure of mouse lung and adult human lung tissue culture to marijuana smoke in vitro resulted in abnormal cell proliferation and abnormalities in DNA content (Leuchtenberger and Leuchtenberger, l97l; Leuchtenberger, et al., l973b). Addition of A-9-THC and olivetol, a compound with a ring structure similar to cannabinoids, to normal human leukocyte cultures induced hypodiploidy (defined as metaphase nuclei with a chromosome complement of less than 30 chromosomesâa normal human cell contains 46 chromosomes) (Morishima et al., l976). Hybrid mice treated for 5 consecutive days with A-9-THC, cannabinol, and cannabidiol at a dose of l0 mg/kg had a three- to fivefold increase of micronuclei over controls. The number of micronuclei increased with increasing A-9-THC dosage. Examina- tion of bone marrow mitosis in these same mice showed a five- to sevenfold increase in chromosome number aberrations during metaphase (Zimmerman and Raj, l980). Human Studies Studies of lymphocytes cultured from human marijuana smokers defined either as "moderate" users (at least one marijuana cigarette per week, range l-l0 for a minimum of two years) or "heavy" users (more than three times per week) all of whom consumed between l2.9 and l5.3 marijuana cigarettes per day during the experiment, turned up a significantly larger number of cells with less than 30 chromosomes than would be found in normal control cultures (Morishima et al., l979). These positive findings suggest that marijuana may affect chromosome segregation during cell division and result in cells with fewer than the normal number of chromosomes. What these findings mean in terms of risk for abnormalities in offspring or possible disease is not known. Findings in lymphocyte cultures may not be relevant to what is happening in the germ cells (sex cells).
l03 THE IMMUNE SYSTEM The immune system functions in protecting the body against viruses, bacteria, and other infections. It also plays a major role in preventing the growth and dissemination of cancerous cells. There have been reports that cannabis is immunogenic, capable of activating components in the immune system. These components include such cells as lymphocytes, some of which produce antibodies in response to invasion by a foreign agent, and macrophages, which can be stimulated by inflammation to ingest invaders. Human Studies There have been reports that cannabis interferes with components in the immune system in man. Antibodies will develop in response to marijuana in some people, along with an allergic response, while others develop antibodies without apparent allergic reaction (Liskow et al., l97l; Shapiro et al., l974, l976; Lewis and Slavin, l975). However, the studies reporting these effects were not designed to determine which components of the marijuana are immunogenic and which are allergenic. Studies of various aspects of the immune system in persons who were chronic users of marijuana have indicated mild decreases in activity of one or another component of the system; however, other investigators have noted no changes outside of the normal range (Gupta et al., l974; Petersen et al., l975, l976; White et al., l975; Lau et al., l976; Rachelefsky et al., l976; Silverstein and Lessin, l976; Cushman and Khurana, l977; McDonough et al., l980). These apparent inconsistencies may stem from the variability in the amount of marijuana consumed among users in different studies and the differences in the immune system assays. Hashish, as distinct from marijuana, was shown to have a slight temporary stimulatory effect on the immune system (Kaklamani et al., l978; Kalofoutis et al., l978). Animal Studies A number of studies have shown that A-9-THC and other cannabinoids induce immunological defects in rodents (Petersen and Lemberger, l976; Lefkowitz and Klager, l978, Lefkowitz et al., l978; Preuss and Lefkowitz, l978). The doses varied from 5 to 25 mg/kg (intra- peritoneally) to l00 mg/kg (orally). At the higher doses there was a diminution of immune response, as measured by standard immunological assays. Delta-9-THC had the same effects on cells grown in vitro. Other cannabinoids also have been tested for their effects. Cannabinol, A-e-THC, and l-methyl-A-8-THC had the same immunosuppressive effects as A-9-THC, but cannabidiol had no immunosuppressive effect. Immunizing rabbits with A-9-THC resulted in the production of antibodies (Chiarotti et al., l980).
l04 BODY TEMPERATURE Regulation of body temperature is a complex process that can be influenced by drugs. In several species of animals, A-9-THC produces a lowering of body temperature (hypothermia). The effect is seen when animals are housed at normal room temperatures, and it is greater with colder ambient temperatures (Pertwee and Travendale, l979). Marijuana apparently causes a decrease in heat production for reasons that are unclear. In experiments with human subjects, marijuana has produced little or no change in body temperature when given in a cool environment (Beaconsfield et al., l972; Hanna et al., l976). In a hot environment (40°C) marijuana caused inhibition of sweating and a consistent rise in body temperature (Jones et al., l980). Thus, there is evidence that marijuana does interfere with temperature regulation, although there is no currently known clinical significance to this finding. Cannabis appears to interfere with temperature regulation, but the clinical significance is unknown. SUMMARY Male Reproductive Function In animals, marijuana and its derivatives can acutely lower gonadotropic secretion when administered intraperitoneally. There is also some evidence in animals to suggest that these agents can directly affect the seminiferous tubule. In man, sperm number and motility are decreased during chronic marijuana use. From the available studies, it appears this was due to a direct effect of the cannabinoids either on the seminiferous tubular epithelium or the epididymal sperm. Due to conflicting and incomplete evidence, it is not possible to conclude at the present time whether marijuana smoking has a significant effect upon gonadotropic and testosterone concentrations in humans. Whether the decrease in sperm number or motility has any effect on fertility is not known. Female Reproductive Function There is only one study of human beings that attempts to establish the endocrine profile and menstrual patterns of women who used marijuana on a chronic and frequent basis. By combining categories of anovulation and shortened luteal phase, a statistically significant difference was noticed in the marijuana using group. It is not known if this leads to problems with fertility or lactation, or if it leads to cancer of the reproductive organs. Animal studies have shown that A-9-THC lowers the serum gonadotropic levels. It is unknown if there is a direct effect on the reproductive tissues, particularly under prolonged use of cannabis products.
l05 Birth Defects and Teratogencity Cannabis is teratogenic at high doses in animals. There is no evidence of obvious teratogenicity or structural defects in the offspring of human users. But the data are not adequate to reveal a long-range functional impairment or a very low level of terato- genicity if one is present. It may be impossible to identify a distinct role for cannabis in the production of subtle effects in offspring, because of the confounding influences of malnutrition, smoking, and alcohol. Genetic Effects Marijuana and &-9-THC do not appear to break chromosomes, although there is some conflicting evidence on this point. Multiple drug use seems to be correlated with an increase in the numbers of gaps and breaks in the genetic material. Furthermore, marijuana may affect chromosome segregation during cell division, resulting in abnormal numbers of chromosomes in daughter cells. While these conflicting results are worrisome, their clinical significance is not known. Further investigations, especially controlled prospective studies, of human beings are needed. The Immune System The data from animal studies suggest that A-9-THC and some of its analogues have a mild, transient, immunosuppressant effect in both in vitro and in vivo systems; the effects are mild compared with known immunosuppressant drugs. The studies in human beings are contradic- tory; some demonstrated mild, immunosuppressive effects, but others, using the same or similar methods, did not find any differences in the immune system between normals and chronic marijuana smokers. At the present time, there have been no human or animal studies that have determined if marijuana smokers are more prone to infections or other diseases. Because of the widespread use of marijuana, even weak immunosuppressive effects are a concern. Since further research may not demonstrate definitive findings, imrnunologic effects should be studied along with other variables in a larger investigation. If marijuana is to be used on immunosuppressed patients (for example, for antiemetic purposes during cancer chemotherapy), even minor additional suppression might be dangerous. RECOMMENDATIONS FOR RESEARCH The committee recommends the following types of studies. * Further observations should be made regarding the relation of marijuana use to reproductive defects in human beings, especially
l06 on young users whose reproductive biology is undergoing rapid change. The principal need is for assessment of endocrine profiles and semen analysis in male users versus nonusers, with adequate control of confounding variablesâfor example, diet, alcohol, other drug use. In women, the principal need is for more data on endocrine and menstrual patterns in users versus nonusers, with particular attention to the length of cycles, the presence or absence of ovulation, and the existence or absence of subfertility. More studies are needed to detect subtle, low-frequency, or cumulative effects on reproductive function in long-term, heavy users. * Although routine testing of teratogenicity in human beings is not recommended at this time, the collection of precise epidemiologic information on the outcome of human pregnancy in marijuana users is of great importance and must be carefully controlled. * There are no good animal models for studying the effects of smoking marijuana, but cytogenetic studies in animals after exposure to A-9-THC by other routes than smoking would be of some value. The most relevant studies still would be in vivo human studies. * Marijuana has been found to have mild immunological effects in a variety of test systems, but studies of its influence on the body's immune defense against microorganisms are lacking and need to be conducted. * Critical experiments are needed to test the hypothesis that A-9-THC causes disruption of thermoregulatory effector responses rather than an alteration of the level of thermoregulation. ' Inherited variation in the way some drugs are metabolized is widely recognized. This type of variation must be evaluated in respect to susceptibility to marijuana. REFERENCES Asch, R.H., Fernandez, E.G., Smith, C.G., and Pauerstein, C.J. Precoital single doses of A-9-tetrahydrocannabinol block ovulation in the rabbit. Fertil. Steril. 3l:33l-334, l979. Asch, R.H., Smith, C.G., Siler-Khodr, T.M., and Pauerstein, C.J. Effects of A-9-tetrahydrocannabinol during the follicular phase of the Rhesus monkey (Macaca mulatta). J. Clin. Endocrin. Metab. 52:50-55, l98l. Ayalon, D., Nir, I., Cordova, T., Bauminger, S., et al. Acute effect of A-i-tetrahydrocannabinol on the hypothalamo-pituitary- ovarian axis in the rat. Neuroendocrinology 23:3l-42, l977. Bauman, J. Marijuana and the female reproductive system, pp. 85-88. Testimony before the Subcommittee on Criminal Justice of the Committee on the Judiciary, U.S. Senate, "Health Consequences of Marihuana Use," January l6-l7, l980. Washington, DC: U.S. Government Printing Office, l980. Bauman, J.E., Kolodny, R.C., Dornbusch, R.L., and Webster, S.K. Efectos endocrinos del uso cronico de la mariguana en mujeres,
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