The National Football League prohibits the use of marijuana as part of its broader, long-standing program to prevent substance abuse. It also imposes stiff penalties on players caught breaking the rules.

In the lead-up to the Super Bowl, in which it so happens both teams hailed from states that recently legalized marijuana for recreational purposes, pressure mounted on the league to reconsider its ban. A group called the Marijuana Policy Project even bought space on five billboards in New Jersey, where the game took place on Sunday, asking why the league disallowed a substance that, the group says, is less harmful than alcohol.

It's a fair question. Marijuana isn't a performance-enhancing drug, for starters, and more than 20 states have legalized it for medical purposes. The league would merely be catching up to contemporary practice by creating a medical exception.

At a news conference on Jan. 7, the league commissioner, Roger Goodell, did not rule out a change in policy. "I don't know what's going to develop as far as the next opportunity for medicine to evolve and to help either deal with pain or help deal with injuries," he said, "but we will continue to support the evolution of medicine." On Jan. 23, he said the league would "follow medicine and if they determine this could be a proper usage in any context, we will consider that." There is, in fact, a body of evidence indicating a "proper usage": one of particular relevance to a hard-hitting, injury-riddled sport.

"Cannabinoids," the Institute of Medicine reported in 1999, "can have a substantial analgesic effect." NFL medical experts obviously aren't convinced, but NFL players seem to be. HBO's "Real Sports With Bryant Gumbel" estimated in January that 50 to 60 percent of players smoked marijuana, many to manage pain.

Players, of course, have access to other painkillers, including prescription drugs. Yet as former Surgeon General Joycelyn Elders has argued, "marijuana is less toxic than many of the drugs that physicians prescribe every day." As public opinion and state laws move away from strict prohibition, it's reasonable for the NFL to do the same and let its players deal with their injuries as they — and their private doctors — see fit.