Q& A

With medical marijuana on the back burner, what do we know?

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Tuesday, October 27, 2009

Last week, the Justice Department ordered its staff to back off prosecution of people who use marijuana for medical purposes in the 14 states in which such use is legal. The directive reopened a question that has been part of the debate on U.S. drug policy for decades.

To understand more about the drug's medical properties, we turned to Daniele Piomelli, who since 1998 has led a program, funded by the National Institutes of Health, to study the impact of marijuana and other psychoactive drugs on the brain. He is a professor of pharmacology and biological chemistry at the University of California at Irvine as well as and director of the center for Drug Discovery and Development at the Italian Institute of Technology in Genoa.

What medical benefits does marijuana offer? Have these benefits been demonstrated in rigorous scientific studies?

Several controlled clinical trials have been carried out in the last few years, using either smoked marijuana or a mouth spray that contains an extract of the marijuana plant. The results are quite consistent. They show that marijuana improves the well-being of patients with multiple sclerosis and alleviates chronic pain in patients with damage or dysfunction of nerve fibers (so-called neuropathic pain). Other work has shown that marijuana and its active ingredient THC (delta-9-tetrahydrocannabinol) reduce the nausea that accompanies chemotherapy, stimulate appetite in AIDS wasting syndrome and lessen tics in Tourette's syndrome. By and large, the use of marijuana in these trials was associated with few and mild side effects (for example, dry mouth and memory lapses).

What are the risks of medical use of marijuana? Could it become addictive or lead to use of other, more dangerous drugs?

Marijuana can produce dependence, though less aggressively than, say, tobacco or the so-called opiate painkillers. Frequent use is risky, however, particularly during adolescence when the neural circuits in the brain are still maturing. It turns out that the brain employs its own marijuana-like substances, called endocannabinoids, to send signals from one neural cell to another, and that THC mimics these substances. The endocannabinoids seem to be very important in brain development, so messing with them before the nervous system becomes fully mature is not a smart thing to do.

There is little hard evidence that using marijuana leads to the subsequent use of other addictive drugs. On the other hand, it is becoming increasingly clear that stressful life events (particularly in critical periods such as adolescence) can encourage drug use and facilitate the development of addictions.

How would a marijuana user be sure to get the correct dose of the active ingredient?

It is difficult to say, because the various types of marijuana now available contain widely different concentrations of THC. Standardized marijuana preparations that contain a fixed amount of THC are not currently sold to the public, though the National Institute on Drug Abuse does provide them to investigators for use in clinical trials.

Is there an alternative way to get the same ingredient in some other form?

A clinical form of THC was approved by the Food and Drug Administration many years ago. It is marketed under the name of Marinol and is used to treat nausea in cancer patients undergoing chemotherapy as well as loss of appetite in AIDS patients. It comes in capsules and is taken orally. Many medical marijuana users say the fixed dose of oral THC creates a problem; they say they prefer smoked marijuana because its dosage can be adjusted simply by changing the length and intensity of the puffs. They may be right, but the burning of a marijuana joint creates tars and other toxic chemicals that can be harmful with prolonged exposure. An alternative is to use so-called smokeless delivery systems such as vaporizers and sprays.


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