I am not so sure the situation regarding pot is so clear cut. The US Gov't has produced pot itself, and handed it out for legally sanctioned experiments. It has also provided pot for the treatment of glaucoma (ended by Bush in 1992).
Note,in the wikipedia article below, seven patients are still recieving pot from a federal pharmacy. Are those seven people banned from owning firearms?
Origin
"Medicinal Cannabis farmed by the University of Mississippi for the governmentThe Compassionate Investigational New Drug Study program began in 1978 after a lawsuit was brought against the Food and Drug Administration, Drug Enforcement Administration, National Institute on Drug Abuse, Department of Justice, and the Department of Health, Education & Welfare by Robert Randall (Randall v. U.S). In 1976, Randall, afflicted with glaucoma, had successfully used the Common Law doctrine of necessity to argue against charges of marijuana cultivation because it was deemed a medical necessity (U.S. v. Randall). On November 24, 1976, federal Judge James Washington ruled:
While blindness was shown by competent medical testimony to be the otherwise inevitable result of the defendant's disease, no adverse effects from the smoking of marijuana have been demonstrated. Medical evidence suggests that the medical prohibition is not well-founded.
The criminal charges against Randall were dropped, and following a petition (May 1976) filed by Randall, federal agencies began providing him with FDA-approved access to government supplies of medical marijuana, becoming the first American to receive marijuana for the treatment of a medical disorder. Randall went public with his victory and shortly after the government tried to prevent his legal access to marijuana. This led to the aforementioned 1978 lawsuit where Randall was represented pro bono publico by law firm Steptoe & Johnson. Twenty-four hours after filing the suit, the federal agencies requested an out-of-court settlement which resulted in Randall gaining prescriptive access to marijuana through a federal pharmacy near his home.
The settlement in Randall v. U.S. became the legal basis for the FDA's Compassionate IND program. Initially only available to patients afflicted by marijuana-responsive disorders and orphan drugs, the concept was expanded to include HIV-positive patients in the mid-1980s. Due to the growing number of AIDS patients throughout the late 1980s and the resulting numbers of patients who joined the Compassionate IND program, the George H. W. Bush administration closed the program down in 1992. At its peak, the program had thirty active patients.
[edit] Compassionate IND today
The remaining patients in the Compassionate IND program were grandfathered in. There are only seven surviving patients in the program today (two remain anonymous). What follows is a table with details of the five surviving patients who are not anonymous, and details of the case as known relating to each patient"