Medical-marijuana is legal in some states, but a number of organ-donation programs bar users from getting transplants even though marijuana does not have direct negative effects on most organs, the Associated Press reported April 27.

Medical-marijuana patient Timothy Garon, 56, has hepatitis C but was recently refused a spot on the liver transplant list at the University of Washington Medical Center because he uses the drug. Transplant programs often bar patients with a history of alcohol or other drug use from getting a replacement organ.

"Marijuana, unlike alcohol, has no direct effect on the liver. It is however a concern ...  in that it's a potential indicator of an addictive personality," said Robert Sade, director of the Institute of Human Values in Health Care at the Medical University of South Carolina.

Transplant policies are left to individual hospitals, and some automatically reject anyone who uses illicit substances; others, like the UCLA Medical Center, allow patients to join their transplant list if they have been clean and sober for six months. Some insurers also require proof of abstinence before they will pay for a transplant.

Some experts have called for national eligibility standards that could take into account medical-marijuana laws.

Post-transplant, doctors generally agree that smoking marijuana should be prohibited, since the drugs patients take to prevent organ rejection increase the risk of a potentially deadly infection that can be triggered by mold in marijuana and tobacco.