New Scientist Marijuana Special Report - Introduction

Aerosols: the future of the spliff?
From pain relief to stimulating the appetites of patients on chemotherapy, marijuana seems to have plenty going for it as a medicine. But many doctors worry about the weed's effects on lungs, and some would rather it didn't get people quite so stoned. For them, the dream solution would be some kind of aerosol or smokeless cigarette filled with a redesigned version of the drug that doesn't bend minds.

The first part of the dream is already being worked on -- the second will be harder to achieve. For years, doctors have been allowed to prescribe a swallowable capsule containing the main active ingredient of cannabis, delta-9-tetrahydrocannabinnol (THC). The problem is that patients complain of side-effects such as anxiety and say they prefer to smoke grass because that way they can control the dose through careful inhaling. Some esearchers think they can improve matters by developing an aerosol form of THC.

Even if it works, though, the spray would still make people high, and changing that won't be easy. The problem is cannabis's peculiar pharmacology. In the past decade, researchers have discovered that all cannabis's main effects -- from changes in pain perception to euphoria and the munchies -- are the work of a single type of receptor, copies of which protrude from neurons scattered far and wide in the brain. This is a problem because normally researchers fine-tune the effects of drugs by tailoring them to home in like a smart bomb on a small subset of the receptors they usually stimulate. For cannabis and THC, there is no subset. The targets are all identical.

One solution might be to develop drugs that bypass these identical surface receptors and mimic chemical changes triggered by cannabis deeper in cells. But this is a long way off. In the meantime, there is a more basic puzzle to solve: why the brain has cannabis receptors in the first place.

A few years ago, researchers discovered a cannabis-like substance in the brain called anandamide (after the Sanskrit for "bliss"). Like THC, anandamide stimulates cannabis receptors to dampen the electrical activity of neurons and reduce the flow of neurotransmitters across synapses. But nobody has a clear idea why. The best guess is that the brain uses anandamide as a central fine-tuner of electrical activity.

From New Scientist, 21 February 1998