Chromosome Damage due to administration of cannabinoids has been studied at some length. There is great uncertainty as to the clinical significance of existing test tube studies. Whereas Nahas, a researcher long known for his negative interpretations of cannabinoid research, concluded that, “cannabinoids and marijuana may exert a weak mutagenic effect.” A less biased researcher reviewing the same evidence gave an entirely different interpretation, noting that in vivo and in vitro exposure to purified cannabinoids or cannabis resin failed to increase the frequency of chromosomal damage or mutagenesis.
Splitting hairs over inconclusive evidence of chromosome damage caused by excessive doses of cannabinoids may fuel some scientific careers, but conclusions resulting from such speculation are easily discounted. Test-tube methods of creating chromosome breaks with cannabinoids could be duplicated with aspirin, Valium, and many other pharmaceutical drugs. Moreover, DNA samplings of large populations of heavy users in cannabis-friendly countries have failed to show any abnormalities in chromosome structure.
Hollister states that, “virtually every drug that has ever been studied for dysmorphogenic effects [chromosome interference leading to birth defects] has been found to have them if the doses are high enough, if enough species are tested, or if treatment is prolonged.”  Other scientists conclude that, “the few reports of teratogenicity in rodents and rabbits indicate that cannabinoids are, at most, weakly teratogenic in these species.” According to the United Nations World Health Organization report of 1997, “There is not a great deal of evidence that cannabis use can produce chromosomal or genetic abnormalities in either parent which could be transmitted to the offspring.” 
Related sections: Cancer, Immune Responses.
 “The health and psychological consequences of cannabis use.” Chapter 6, National Drug Strategy Monograph No. 25, Australia
 Hollister, “Health aspects of marijuana.” Pharmacological Review, Vol. 38, No. 1, 1986
 Bloch, et al., quoted in Hollister, op cit
 World Health Organization Project on Health Implications of Cannabis Use, 1997