A sample of Blue Dream Boutique marijuana at Takoma Wellness Center in Washington in 2015. (Sarah L. Voisin/The Washington Post)

JUNE 30 could be a red-letter day for federal policy on marijuana: The Drug Enforcement Administration has promised to decide “in the first half of 2016” whether to change the drug’s status under the Controlled Substances Act. At present, it is on Schedule 1, meaning it has “no currently accepted medical use and a high potential for abuse” and is among “the most dangerous drugs . . . with potentially severe psychological or physical dependence,” according to the DEA. Other Schedule 1 drugs include heroin and ecstasy; and for many people, including those who have petitioned the DEA to “reschedule” pot, marijuana simply doesn’t belong in that category — because it isn’t that dangerous, and because, they argue, it has medicinal uses.

Then again, June 30 could bring a ratification of the status quo; the DEA has rejected three previous pot rescheduling petitions, citing factors such as U.S. obligations under international anti-drug agreements and, most important, insufficient evidence of medical usefulness. Specifically, the Food and Drug Administration has never found marijuana safe and effective as a medicine — claims by patients and state “medical marijuana” laws notwithstanding.

The FDA has signed off on a synthetic version of pot’s active ingredient, THC, to treat appetite loss and chemotherapy-induced nausea. It’s not clear, however, how the FDA is supposed to assess a plant-based substance that comes in myriad forms and has more than one active ingredient, deliverable as smoke, a solid or a liquid of different strengths. Those who discount such concerns may have the interests of suffering patients at heart. They may underestimate, however, the pitfalls of promoting a substance that is less destructive than, say, heroin but may be no more useful, medically, than snake oil.

To be sure, this presents a Catch-22: The DEA can’t reschedule marijuana without more research on its potential medical aspects; yet such research is effectively discouraged by keeping it on Schedule I. To date, the federal government has imposed severe limits on the kinds of clinical trials that might lead to FDA approval of certain uses of pot, based on the assumption that it has no medical use.

A better approach would be for Congress to create a new schedule for drugs such as pot that are risky to use but less dangerous than others in Schedule I and that are thought to have medical uses but require more research. A bill proposed last year by Rep. Andy Harris (R-Md.) would create that category and call it Schedule IR. (The R is for “research.”) The idea is to make it easier for scientists to obtain marijuana and organize studies than it is in the current regulatory environment. Mr. Harris’s bill is consistent with policy statements by the American Medical Association and American Academy of Pediatrics, both of which favor more research. It had bipartisan support but got shot down on a procedural vote. Lawmakers should give the measure a second look as soon as possible.