For more than 4,000 years it was used medicinally. Then in 1942 medical marijuana was banned in the United States, but that's not the end of the story. Today, patients with illnesses like cancer, AIDs and MS say it relieves pain and reduces nausea from their meds, and is the only thing that got them through.
Brian Klein takes three pills twice a day for HIV. He's also recovering from Hepatitis C.
"It was pretty devastating getting both at the same time," Klein said.
Hep-C meds are known for their severe side effects -- like nausea. Klein tried lots of treatments to relieve it, but only one worked - marijuana.
"Within a few minutes I could go eat, whereas before, before using it, I couldn't even keep down water. So it was amazing, dramatic difference," Klein said.
A study on Hep-C patients showed smoking pot made them three-times more likely to get rid of the virus, because it got them through treatment.
"If there's a patient for whom that medicine doesn't work, and they do get benefit from marijuana, then that could really be the difference between life and death."
Donald Abrams is a long-time HIV researcher and oncologist and has studied the use in patients.
"When we talk about the side effects, if you will, of marijuana compared to many, many prescription drugs that doctors prescribe on a daily basis, it's really quite safe," Abrams said.
But although medical marijuana is allowed in 12 states, the federal government has declared it "is not medicine" and "not safe." Opponents believe much more research is needed and that it's linked to a higher risk of cancer, heart attack and brain damage.
For Klein, it was a short term fix. He's free of the Hep-C virus and has the energy to do simple things like read and even exercise.
"This was relieving my nausea, and it worked. And I didn't need it for anything more or less," Klein said.