Voters may have overwhelmingly approved medical marijuana by constitutional amendment last week. But all the state’s major physician groups—including the Kansas City Medical Society, of which Mammen is president—opposed every marijuana measure on the ballot.

Now the amendment’s passage makes doctors the gatekeepers of legal marijuana in Missouri, a role most of them didn’t want. And if other states are any indication, a small minority of doctors will be willing to recommend medical marijuana, and those who do may have booming businesses.

Most doctors don’t think of marijuana as medicine, at least not in its raw plant form.

The medical groups say that although certain parts of the cannabis plant have legitimate medical uses, medical marijuana programs like Missouri’s provide access to products that aren’t sold in standard dosages or purities.

Essentially, patients don’t know what they’re getting, so it’s impossible for doctors to measure the risks against the benefits. The marijuana card, therefore, becomes more like a permission slip than a prescription.

Mammen said he prescribes medications derived from plants all the time, including some derived from parts of the cannabis plant. But those are regulated, standardized products vetted by the Food and Drug Administration, not a raw plant of unknown composition.

Still, he said he expects doctors will soon have patients asking them to sign off on their applications for marijuana cards from the Missouri Department of Health and Senior Services.

“If you follow what’s happened in other states, that’s very typical,” Mammen said. “Based upon the publicity, individuals will go to their physicians and ask for marijuana, which actually puts physicians in a little bit of a difficult spot because there’s a lack of data to indicate when is a potentially good time, if there is one, to be able to suggest the use of marijuana.”

Marijuana research has been hampered because the federal government deems it a Schedule I controlled substance. But it has shown promise in treating pain and psychiatric or neurological disorders like Parkinson’s disease, and some parts of the plant have already been incorporated into FDA-approved products for treating epilepsy and for nausea caused by chemotherapy.

But Mammen said marijuana, like other drugs or even herbal supplements, can interact dangerously with other medications patients might be taking, and doctors also need to be concerned about side effects like vomiting or, for people with mental illness, psychotic episodes.

He said he hopes that when the state develops a medical marijuana application form, it doesn’t ask doctors to explicitly recommend marijuana, but rather just asks them to confirm that patients have conditions that qualify them for the card.