Doctors once treated alcoholism with heroin. Now, they want to treat heroin addiction with marijuana.

What accounts for these cycles of enthusiasm and disappointment? Historian David Courtwright of the University of North Florida emphasizes that medicine is surprisingly prone to fads. “Physicians like new drugs. When one becomes available it often gets overused. In the 1970s, for example, physicians prescribed Valium for a wide range of conditions, from anxiety to insomnia to muscle spasms. Quite a few patients became dependent.” Not incidentally, Valium was a benzodiazepine, a class of drugs that had been marketed as safer alternatives to barbiturates, a previous wonder drug that also proved to be addictive and dangerous.

The experience of patients also plays a role in persuading people that a drug is a miracle cure. Because using addictive drugs feels good in the short term (that’s why they are addictive), it can seem to patients with an enormous range of illnesses that addictive drugs are making their illness better. In some cases this is true: A certain extract of marijuana appears to reduce epileptic seizures, for example (prior Wonkblog coverage here). But in other cases the underlying condition is as bad as ever and the positive feelings that the patient is interpreting as successful treatment are really just the psychoactive reinforcement of the addictive drug.