Abusable drugs are regulated by federal law pursuant to treaty obligations. Since pharmaceuticals are sold in interstate commerce, their regulation is also a federal matter. But the practice of medicine is regulated by the states.

Cannabis is an abusable drug with therapeutic properties. (Sativex, an extract containing all the active agents in whole cannabis, is now an approved drug in Canada.)

Cannabis can easily be produced locally, with no interstate commerce involved.

Several states have laws designed to make cannabis, despite its status as a Schedule I controlled substance under Federal law, available to patients whose physicians want them to have it for therapeutic purposes. California has gone the farthest down this road, with more many hundreds of "dispensaries" -- in effect, retail outlets -- now in operation, and physicians allowed to "recommend" cannabis for any condition or symptom, even something as unspecific as "anxiety."

The California system has become an open joke, with physicians advertising themselves as "herbal recommendationists" and promising that if a visit doesn't lead to a recommendation there will be no fee. As a result, the "medical" market now makes up a substantial fraction of the total cannabis market in California, with revenues estimated in the hundreds of millions of dollars per year.

The precise shares of the "medical" cannabis market made up by (1) truly sick people with conditions cannabis might help - MS patients with spasm, HIV patients in search of appetite enhancement, chemotherapy patients fighting nausea - (2) chronic users in effect getting maintenance doses for their cannabis dependency, and (3) frankly non-medical users remains unknown, but few believe that the first category accounts for as much as 10 percent of the (massive) volume of the "medical" cannabis industry.

Those efforts have, naturally, led to conflict between state and federal governments. The Supreme Court struck down a DEA effort to strip physicians of the federal licenses they need to prescribe controlled drugs as punishment for recommending that their patients use cannabis. But it later ruled in Gonzales v. Raich that the California statute did not protect either providers or recipients of cannabis from federal prosecution.

Attorney General Eric Holder, in a decision announced in February and recently formalized as policy guidance for Justice Department agencies, has decided that prudence (and perhaps comity, though he did not say so) dictate that the federal government should decline to use the power that the Raich decision found it to have.

In states such as New Mexico and Rhode Island, which are attempting to establish well-controlled processes to get cannabis to patients, the announcement removes the specter of federal intervention, and may even allow providers there to establish overt growing operations rather than buying supplies from what remains a completely illegal growing industry.

In California, where the legal status of the dispensaries remains in dispute, it may be hard to figure out which activities are actually in full compliance with state law and therefore exempt from federal enforcement actions under the new policy. California law allows growing by patients and their care-givers, and the formation of cooperative enterprises, but not (in black letter) proprietary enterprises, which most of the dispensaries appear to be.

Neither "medical marijuana" advocates nor federal officials seem to have any interest in handling this problem in straightforward fashion: doing the clinical research required to establish the safety and efficacy of some standardized cannabis product for some specified medical condition, thus making it a prescription drug and a Schedule II controlled substance, available by prescription and sold through pharmacies. The federal government continues to use its legal monopoly on research cannabis (which it claims for no other controlled substance) to obstruct the necessary studies, while the advocates so far have not been willing to spend any fraction of the millions of dollars spent on litigation and the promotion of ballot initiatives (let alone the much larger sums flowing through the dispensary system) to performing research in foreign countries where research cannabis is easily available.

Ironically, cannabis as a prescription drug would be much less available in California than it is today. If medical need could be met though ordinary pharmacies, there would be no justification for the proliferation of retail cannabis outlets. Actual prescriptions for the drug would be much harder to obtain than the transparently pretextual "recommendations" now being issued by the bushel to any "patient" with $75.

The larger question, of course, involves legalization for explicitly non-medical use; an initiative measure to that effect is expected to be on the ballot in California next year. Federal forbearance toward state-approved activities that violate the Controlled Substances Act seems unlikely to extend to outright legalization, so if the legalization initiative were to pass the federal-state struggle that the Attorney General's new policy was designed to end might be revived.