The decision means that physicians who help someone in Oregon commit suicide will not risk losing their federal licenses to write prescriptions.
Reno reversed the position initially taken by the head of one of her own agencies, the Drug Enforcement Administration, which had said that doctors who prescribe drugs under Oregon's assisted-suicide law could face severe sanctions.
It wasn't clear whether the decision would foretell a national policy initiative. But it would clear the way for doctor-assisted suicide in Oregon, where voters twice have approved a law allowing doctors to prescribe lethal doses of drugs for patients with less than six months to live. It is the nation's first doctor-assisted suicide law.
Legal challenges and the reluctance of the Justice Department to issue an opinion about the Oregon law had made doctors and hospitals wary.
At a November meeting of the Oregon Medical Association's governing body, doctors said they were concerned about implied threats from Congress and the Drug Enforcement Administration to restrict prescriptions for controlled substances.
Although the Justice Department began reviewing its jurisdiction over assisted suicide in November 1997, the Oregon law attracted widespread attention in Washington after the first reports of an assisted suicide surfaced last March.
The news sent a shock wave through Congress, prompting dozens of members to write to Reno. Most urged her to accept an interpretation of the Controlled Substances Act that would disqualify assisted suicide as a "legitimate medical purpose" of drugs.
The long wait for the Justice Department opinion did not stopped the assisted-suicide law from being used. At least three terminally ill Oregonians - including a cancer-stricken grandmother in her 80s - have killed themselves with lethal prescriptions since November.
Sen. Ron Wyden, D-Ore., said that while he voted against the assisted-suicide measure, the decision by Reno is "a victory for democracy."
"Oregon now faces a challenge to redouble our efforts to make certain that Oregonians have better options for health care at the end of their lives," he said in a statement.
He said that is the best way to make sure assisted suicide remains a rarity in Oregon.