No doubt I have forgotten much pharmacology since I was a student, but one diagram in my textbook has stuck in my mind ever since. It illustrated the natural history, as it were, of the way in which new drugs are received by doctors and the general public. First they are regarded as a panacea; then they are regarded as deadly poison; finally they are regarded as useful in some cases.

It is not easy to say which of these stages the medical use of cannabis and cannabis-derivatives has now reached. The uncertainty was illustrated by the on-line response from readers to an article in the latest New England Journal of Medicine about this usage. Some said that cannabis, or any drug derived from it, was a panacea, others (fewer) that it was deadly poison, and yet others that it was of value in some cases.

The author started his article with what doctors call a clinical vignette, a fictionalized but nonetheless realistic case. A 68-year-old woman with secondaries from her cancer of the breast suffers from nausea due to her chemotherapy and bone pain from the secondaries that is unrelieved by any conventional medication. She asks the doctor whether it is worth trying marijuana since she lives in a state that permits consumption for medical purposes and her family could grow it for her. What should the doctor reply?

The scientific evidence about the medical benefits of cannabis is suggestive but not conclusive, in large part because governments have placed legal obstacles in the way of proper research, but also because the smoke of marijuana contains so many compounds that need to be tested individually. But it seems that cannabis can relieve nausea (one of the most unpleasant of all symptoms when it is persistent) and some kinds of pain. Its side effects in this context are unlikely to be serious or severe. To worry about the addictive potential of a drug, for example, when the patient is unlikely to survive very long is clearly absurd, though one doctor did raise the question. I remember all too clearly the days when patients who were dying were denied pain relief by heroin because it was supposedly so addictive.

As soon as the subject of cannabis comes up, passions are aroused that seem to make it impossible for people, even doctors, to stick to the point. One correspondent pointed out that a half of American schoolchildren had tried cannabis, but this was irrelevant even to the irrelevant point he was trying to make. No one, after all, suggests that there should be no speed limits because almost every driver breaks the law within thirty seconds of starting out. There may be arguments for the decriminalization of cannabis but this is not one of them.

The author of the article comes to the conservative conclusion that doctors should prescribe cannabis medicinally only when all other treatment options (including the much more dangerous oxycodone) have failed. This might seem contradictory. If cannabinoids should prove as effective in some situations as opioids they would be drugs of first rather than last resort.

But it is unlikely in any case that all doctors will remain conservative for long or will prescribe cannabinoids only as a last resort. In Britain in the 1950s doctors were permitted to prescribe heroin for heroin addicts. A very small number of them began, either for payment or because they believed that the “recreational” use of heroin was harmless or even a human right, to prescribe very liberally. The number of addicts increased very quickly, but whether it would have done so anyway is now impossible to say.

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Images courtesy shutterstock / Andre Blais / Andre Blais / 

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