By Susan Greenfield
Oxford, England — Across Europe and America, the legalization of cannabis for personal use generates intense debate.
Britain has, to all intents and purposes, practically decriminalized marijuana usage.
As a neuroscientist, I am concerned. One common justification for legalization or decriminalization of cannabis centres around the idea that it does not involve a victim. At least four reports in major medical journals — Ramstrom (1998), Moskowitz (1985), Chesher (1995) and Ashton (2001) — show the contrary.
Costs to the community include accidents at work or at home, educational under-attainment, impaired work performance and health-budget costs.
Another argument is over that cannabis is nonaddictive. Of course, defining addiction is hard. But if one regards it as an inability to give up, then there is strong evidence that cannabis incites dependence. Recent scientific papers report many users in the United States, United Kingdom and New Zealand now seek treatment for dependence. Other papers show that 10 percent of users want to stop or cut down but have difficulty doing so. A paper in 1998 reported that 10 to 15 percent of users become dependent on pot.
It was shown recently that withdrawal symptoms were experienced after only three days of light use. Heavy users confront a worse situation. Dr. Bryan Wells, a rehabilitation expert, says that for the first time he’s beginning to see in heavy cannabis users the withdrawal symptoms produced by hard drugs.
Another argument is the beneficial effect of marijuana on pain. So far, that evidence is anecdotal; it is hard to exclude placebo effects. The results from clinical trials are awaited.
But distinctions should be drawn between recreational drugs and medicines, as they are for opiates. If cannabis is a painkiller, then it must have a huge impact on the physical brain.
Indeed, widespread reports exist of the impact of cannabis on the brain, in particular areas concerned with memory (hippocampus), emotion (mesolimbic system) and movement (basal ganglia). Cannabis affects a variety of chemical systems and it works via its own receptor — its own molecular target.
The fact that there is a naturally occurring analogue of cannabis in the body, as there is for morphine, provides a basic reason to differentiate it from alcohol.
For an agent that affects a variety of transmitter systems, it is as though it were a transmitter itself. This is not surprising, for cannabis has a clear effect on psychology. Not only does it produce euphoria, but the effects, often overlooked, may also include anxiety, panic and paranoia. Disorders in psychological performance, attention impairments and memory deficits are well known.
More disturbing — and less frequently acknowledged — is the fact that these effects can be long-term.
In one recent study, the attention spans of ex-users were compared to those of current users, short-term and long-term. The abstainers, who had been users for at least nine years, had quit from three months to six years before the study. Of the current users, one group had at least 10 years of dependence; the other, about three years. Everyone in the study had used cannabis from 10 to 19 days per month.
Although the quitters did better than users, all had attention impairments in comparison with nonusers in a control group. The impairment was related to the duration of use. Most disturbing was the fact that no improvement in performance occurred with increasing abstinence.
It was no surprise, then, that because these long-term effects seem to be irreversible, there is an effect on brain pathology. Because much of this data comes from work with isolated systems, and therefore on all brains, an obvious criticism is that you can’t extrapolate from such data. Yet, the evidence suggests that the long-term effects must have a physical basis. Is there a safe dose of cannabis, with no effect on the brain? Even a dose comparable to one joint, and analogous levels of the active THC ingredient to that in plasma, can kill 50 percent of neurons in the hippocampus (an area related to memory) within six days. People are unaware that the THC in cannabis remains in the body for more than five days. For someone using cannabis routinely, the dose carried in the body is higher than they imagine. It is easy to underestimate the dose because of the wide range in the strength of cannabis. Individual variations in body fat and, worryingly, variations in one’s disposition to psychosis, mean that you cannot predict how much cannabis will affect any person at any time.
Cannabis could well be having a serious effect on the mind, which I define as the personalization of brain circuits that reflect an individual’s experiences. A transmitterlike substance, with such powerful effects, must affect those circuits. So blowing your mind might be exactly what marijuana users are doing.
Source: San Francisco Chronicle (CA): Pubdate: Sun, 6 Jan 2002
Note: Susan A. Greenfield, the Fullerian Professor of Physiology at Oxford University, is director of the Royal Institution of Great Britain. This article was written for Project Syndicate, based in Prague.