Cannabis smoking could cause an 'overdose' of the natural cannabinoid signalling system responsible for regulating sperm structure, vigour and fertility. Dr Herbert Schuel and colleagues believe that abuse of marijuana could directly affect the ability of human sperm to fertilise an egg, and could account for certain types of infertility.

In a study presented today at the annual meeting of the American Society for Cell Biology (San Francisco, 9–13 December 2000), Dr Schuel and his colleagues identified three separate processes in which one of the body's endogenous cannabinoid ligands — anandamide — was disrupted by tetrahydrocannabinol (THC), the major psychoactive constituent of marijuana. Correct levels of anandamide stimulate hyperactivated swimming. When levels become too high, however, hyperactivated motility is inhibited. In addition, increased levels of cannabinoids may inhibit the binding of sperm to the zona and inhibit structural changes over the acrosome.

In the uterus, anandamide regulates development of the...

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