The weed we may all need

My interest in this subject dates back more than ten years. My mother was suffering from cancer, which had spread to the lungs. The disease was growing despite chemotherapy and this was causing increasing breathlessness.

Like most people, my mother wanted to stay in control of any medical decisions that affected her. The usual palliative treatment for breathlessness is low doses of morphine, coupled with small doses of diazepam if there is anxiety. She took neither, preferring to ignore her symptoms. Taking tablets would have reminded her she was not in control.

As a doctor, it is best not to get involved in the care of family. However, I knew my expertise in palliative care would be needed when she was dying. Eventually, the breathlessness became too much to bear and the doctors did not know what to do. Knowing she would not want medication that would make her drowsy, I suggested she try a cannabinoid (a man-made derivative of cannabis) known as nabilone. Within an hour, her breathlessness was relieved and she was still able to get all the answers in a television quiz before the contestants. She died comfortably two days later.

Compiled by the Institute of Medicine in the United States, this report did not disappoint. The editors have combined information from specialists in neuroscience, pharmacology, immunology, drug abuse, cancer treatment, HIV/Aids and eye diseases, as well as evidence from users of marijuana. Their aim was to give a balanced scientific account of the effectiveness of marijuana for treating medical conditions. A timely idea, given the recent pleas from multiple sclerosis sufferers.

The editors and contributors are to be praised for a review that is comprehensive and understandable. For the non-medical reader, the text contains simple explanations of scientific and medical terminology. The concise executive summary is followed by detailed sections on the consequences of marijuana use and abuse. There is information on the problems of marijuana smoking, including the increased risks of cancer, lung damage, chest infections and problems with pregnancy. There is also data about the possible benefits for a variety of painful conditions, nausea and vomiting (which is what nabilone was developed for) and appetite stimulation for people with cancer and Aids. There are sound recommendations for future research. All the information is presented in a balanced way. It was refreshing not to have to plough through "marijuana is the root of all evil" or "the weed will save the world" generalisations.

I was fascinated by the information about how marijuana works, highlighting the interface between so-called "orthodox" medicine and alternative remedies. Marijuana contains several different compounds, notably tetrahydrocannabinol (THC) and other plant-related cannabinoids.

Scientists have discovered these cannabinoids work by acting on receptors that are present on brain cells, as well as other cells in the body. Why do these receptors occur? It is not because the body intuitively knows that some people might use marijuana. It is now clear that there are cells within our bodies that produce cannabinoids naturally, which then act on the receptors. These cannabinoids serve as chemical messengers, but their exact functions are not fully understood.

Even more interesting is the fact that there are at least two different receptors. One receptor occurs mainly in the brain. Stimulation of this receptor is probably responsible for the psychological effects of THC and some other cannabinoids. Another receptor is found on the white cells that cause inflammation or fight infection. Cannabinoids that activate only this receptor have been discovered. This raises the possibility of developing cannabinoids that could have specific pain-killing or anti-arthritis effects without causing psychological changes.

The authors have assiduously avoided an impassioned debate about the legalisation of marijuana. They point to the evidence that it has a relatively low addictive potential, but balance this with the health risks.It is already possible to get the medical benefits of the cannabinoids without resorting to the use of marijuana, as was the case with my mother. Strong moral views about marijuana should not stand in the way of developing even better cannabinoids for the relief of symptoms such as pain and breathlessness. A similar moral stance for morphine and heroin would have caused immense suffering for millions of people with cancer pain.

Anyone with an interest in marijuana and the scientific process will enjoy this book. As a parent of emerging teenagers, I found the information about marijuana very helpful.

Robert Dunlop is medical director, St Christopher's Hospice, London.