i've posted this before in another similar thread here so i thought it would be relavent here.....
Myth: Pot kills brain cells
Government experts now admit that pot doesn't kill brain cells.(8) This myth came from a handful of animal experiments in which structural changes (not actual cell death, as is often alleged) were observed in brain cells of animals exposed to high doses of pot. Many critics still cite the notorious monkey studies of Dr. Robert G. Heath, which purported to find brain damage in three monkeys that had been heavily dosed with cannabis.(9) This work was never replicated and has since been discredited by a pair of better controlled, much larger monkey studies, one by Dr. William Slikker of the National Center for Toxicological Research(10) and the other by Charles Rebert and Gordon Pryor of SRI International.(11) Neither found any evidence of physical alteration in the brains of monkeys exposed to daily doses of pot for up to a year. Human studies of heavy users in Jamaica and Costa Rica found no evidence of abnormalities in brain physiology.(12) Even though there is no evidence that pot causes permanent brain damage, users should be aware that persistent deficits in short-term memory have been noted in chronic, heavy marijuana smokers after 6 to 12 weeks of abstinence.(13) It is worth noting that other drugs, including alcohol, are known to cause brain damage.
Myth: Marijuana causes sterility and lowers testosterone
Government experts also concede that pot has no permanent effect on the male or female reproductive systems.(14) A few studies have suggested that heavy marijuana use may have a reversible, suppressive effect on male testicular function.(15) A recent study by Dr. Robert Block has refuted earlier research suggesting that pot lowers testosterone or other sex hormones in men or women.(16) In contrast, heavy alcohol drinking is known to lower testosterone levels and cause impotence. A couple of lab studies indicated that very heavy marijuana smoking might lower sperm counts. However, surveys of chronic smokers have turned up no indication of infertility or other abnormalities.
Less is known about the effects of cannabis on human females. Some animal studies suggest that pot might temporarily lower fertility or increase the risk of fetal loss, but this evidence is of dubious relevance to humans.(1) One human study suggested that pot may mildly disrupt ovulation. It is possible that adolescents are peculiarly vulnerable to hormonal disruptions from pot. However, not a single case of impaired fertility has ever been observed in humans of either sex.
Myth: One joint equals one pack of (or 16, or maybe just 4) cigarettes
Some critics exaggerate the dangers of marijuana smoking by fallaciously citing a study by Dr. Tashkin which found that daily pot smokers experienced a "mild but significant" increase in airflow resistance in the large airways greater than that seen in persons smoking 16 cigarettes per day.(7) What they ignore is that the same study examined other, more important aspects of lung health, in which marijuana smokers did much better than tobacco smokers. Dr. Tashkin himself disavows the notion that one joint equals 16 cigarettes. A more widely accepted estimate is that marijuana smokers consume four times as much carcinogenic tar as cigarettes smokers per weight smoked. (8) This does not necessarily mean that one joint equals four cigarettes, since joints usually weigh less. In fact, the average joint has been estimated to contain 0.4 grams of pot, a bit less than one-half the weight of a cigarette, making one joint equal to two cigarettes (actually, joint sizes range from cigar-sized spliffs smoked by Rastas, to very fine sinsemilla joints weighing as little as 0.2 grams). It should be noted that there is no exact equivalency between tobacco and marijuana smoking, because they affect different parts of the respiratory tract differently: whereas tobacco tends to penetrate to the smaller, peripheral passageways of the lungs, pot tends to concentrate on the larger, central passageways.(9) One consequence of this is that pot, unlike tobacco, does not appear to cause emphysema.
Myth: Marijuana causes chromosome and cell damage
According to the NAS,(14) "Studies suggesting that marijuana probably does not break chromosomes are fairly conclusive." Cannabinoids in themselves are neither mutagenic nor carcinogenic, though the tars produced by marijuana combustion are. Some laboratory studies have suggested that high dosages of THC might interfere with cell replication and produce abnormal numbers of chromosomes; however, there is no evidence of such damage in realistic situations.
Myth: Marijuana damages the immune system
A variety of studies indicate that THC and other cannabinoids may exercise mild, reversible immuno-suppressive effects by inhibiting the activity of immune system cells know as lymphocytes (T- and B-cells) and macrophages. It is dubious whether these effects are of import to human health, since they are based mainly on theoretical laboratory and animal studies. According to a review by Dr. Leo Hollister(8) "The evidence [on immune suppression] has been contradictory and is more supportive of some degree of immunosuppression only when one considers in vitro studies. These have been seriously flawed by the very high concentrations of drug used to produce immunosuppression. The closer that experimental studies have been to actual clinical situations, the less compelling has been the evidence."
The immune suppression issue was first raised in research by the notorious cannabophobe Dr. Gabriel Nahas, but a flurry of research by the Reagan administration failed to find anything alarming. The recent discovery of a cannabinoid receptor inside rat spleens, where immune cells reside, raises the likelihood that cannabinoids do exert some sort of influence on the immune system.(9) It has even been suggested that these effects might be beneficial for patients with auto-immune diseases such as multiple sclerosis. Nevertheless, not a single case of marijuana-induced immune deficiency has ever been clinically or epidemiologically detected in humans.
One exception is the lungs, where chronic pots smokers have been shown to suffer damage to the immune cells known as alveolar macrophages and other defense mechanisms.(10) It is unclear how much of this damage is due to THC, as opposed to all of the other toxins that occur in smoke, many of which can be filtered out by waterpipes and other devices(11).
There is no reason to think marijuana is dangerous to AIDS patients. On the contrary, many AIDS patients report that marijuana helps avert the deadly "wasting syndrome" by stimulating appetite and reducing nausea. Cannabinoids do not actually damage the T-cells, which are depleted in HIV patients: one study even found that marijuana exposure increased T-cell counts in subjects (not AIDS patients) whose T-cell counts had been low.(12) Epidemiological studies have found no relation between use of marijuana or other drugs and development of AIDS.(13)
Was actually a really cool experience and a wake up call 
