Addictive cannabis

Professor Heather Ashton does us a considerable service by drawing attention to the much-neglected adverse properties of cannabis ("From hashish to ashes?" THES, April 17).

Recent basic research, which directly complements Professor Ashton's clinical experience, has proved convincingly that cannabis is a drug of dependence.

Neuroscientific studies showed initially that we have within our brains receptors with 3-D specificity for cannabis and also endogenous cannabis-like neurotransmitters similar to serotonin and dopamine. Thus, taking cannabis will inevitably disrupt our endogenous cannabis systems.

Evidence for this comes from studies (Aceto et al, Journal of Pharmacology and Experimental Therapeutics, 1996, 8: 1290-1295) in which rats were treated with cannabis for four days only. This caused the endogenous cannabis system to adapt in order to minimise the effects of the administered cannabis.

The rats were then given a recently developed specific cannabis antagonist drug. This rapidly displaced cannabis from its receptors and "precipitated" a withdrawal syndrome involving abnormal gross movements, shaking and muscle spasms.

Similar effects are seen with opiates (such as heroin and morphine) in animals treated with specific opiate antagonists after opiate experience, which interferes with the functioning of endogenous opiates or "endorphine".

These results show unequivocally that cannabis is a drug of dependence and suggest that its "addictive" properties have been underestimated.

Given the widespread use of cannabis among students, this is cause for considerable concern for all in higher education and a very clear reason for not decriminalising cannabis and marijuana.

Andrew Goudie Reader in psychopharmacology University of Liverpool