Senators voted 21-16 for the proposal from Sen. Fred Mills, R-Parks. It needed 20 votes to pass.
Louisiana hasn't yet started its medical marijuana program, which will eventually get medical-grade pot — in a consumable form that can't be smoked — to people suffering from cancer, glaucoma and a severe form of cerebral palsy.
Mills wants to add seizure disorders, HIV, epilepsy, severe muscle spasms, muscular dystrophy, multiple sclerosis and other diseases to the list.
"It's for people with severe, severe disorders. This is not something you're just going to prescribe haphazardly," Mills said.
Supporters talked of parents struggling to find medications to treat children's seizure disorders and of others struggling through painful diseases.
Sen. Sharon Hewitt, R-Slidell, said a year ago she would never have imagined she would urge support of medical marijuana — but she said she's received 84 emails from people in her district describing how this could help their children with severe medical problems.
"These parents, all they want is an opportunity to be able to help their children. This is life-changing for them," Hewitt said.
Opponents described the bill as a gateway to illegal drug use and, eventually, legalized recreational marijuana.
"Every state they have done this in, teenage drug use has gone up," said Sen. Danny Martiny, R-Kenner. "It's an illegal drug according to the federal law."
The debate now shifts to the House. It faces an uncertain future there, facing opposition from local sheriffs and district attorneys.
Louisiana likely remains years away from getting medical marijuana into people's hands. A state-sanctioned grower hasn't yet been selected.
Under existing law, the state will have one medical marijuana grower and 10 licensed distributors. LSU and Southern University get first right of refusal to grow the medicinal plant. University leaders say they're still determining whether they'll participate. If both schools decline, a public bidding process is opened.