McMahon was one of of a handful of federal patients who received 300 joints a month from the government's secret Compassionate IND (Investigational New Drug) program since 1990.
He was diagnosed with nail patella syndrome, a condition that causes injuries to nails, knees, elbows, hips and other body parts. "I was a pretty good athlete other than I would break things," he once said about growing up. "I have a lot of trouble sitting very long."
Hospitalized in 1988 when he was 38, McMahon was offered a joint by an orderly that helped. "I'd noticed that when I did smoke marijuana I didn't get sick," he said.
Thus began his campaign to find a doctor who would petition the government to allow him to be added to the IND program, which only had four patients at the time.
"I'd noticed that when I smoked marijuana I didn't get sick."
"Five hundred doctors refused to see me, but one wrote back and said it was an interesting case," McMahon explained. "They finally just ran out of reasons. They conceded and we got the first shipment (in 1990). I was taking 10 Percocets a day. I didn't take another pill after that."
However, McMahon said the government weed was "not very good, not very potent." He'd stopped receiving the federal stash in 2013 when his doctor retired.
McMahon founded Iowans for Medical Marijuana with fellow IND patient Barbara Douglass, who died in 2018, and activist Carl Olson. McMahon and Olson were original board members of the advocacy group Patients Out of Time.
Robert C. Randall, who suffered from glaucoma, was the first patient to receive federally-grown marijuana in 1975. He died in 2001. The two last patients on the program are Elvy Musikka, who also has glaucoma, and Irvin Rosenfeld, who's afflicted with bone spurs.
At its height, the IND propram had less than 20 patients. However, in 1992, during the George H.W. Bush adminstration, it stopped admitting new patients.
McMahaon, who ran for vice president as a Grassroots Party candidate in 1996 and 2012, wrote the 2003 book, Prescription Pot: A Leading Advocate's Heroic Battle to Legalize Medical Marijuana. He's survived by his wife Margaret and their three children.