Quinine for leg cramps increases risk of death, study finds

Patients often tell Dr. Kiran V. Patel they've been sipping on quinine water to help ease leg cramps.

Well-meaning relatives and even some doctors recommend it, said Patel, who's the director of neurosurgical pain at Lenox Hill Hospital, in New York.

"But it's an old wives' tale," she told CBS News.

Last year, the U.S. Food and Drug Administration warned against using quinine as an antidote for night-time leg muscle cramps or "restless legs," said Patel. The FDA reported "adverse events with serious outcomes … including 93 deaths" in people who used the remedy. And it wasn't the first time health officials have expressed concerns about quinine. The substance is linked to bleeding and an irregular heart rate. Quinine is only FDA-approved for use as a malaria treatment.

Now, a new study by French researchers has found that in patients who took quinine pills for muscle cramps, there was an increased risk of death.

Dr. Laurence Fardet and colleagues from the Universite Paris Est Creteil looked at long-term outcomes in more than 175,000 adults with muscle cramps, using information from a large U.K. primary care database.

They analyzed data on individuals who had taken 100 milligrams of quinine salt per day or more, and who had used the pills for at least one year between January 1990 and December 2014, and compared them to a larger group of patients who had not used quinine. The follow-up period was about 5.7 years.

Death rates among quinine-takers were higher over time. There were 11,598 deaths (4.2 per 100 person-years) among the 44,699 participants who took quinine compared with 26,753 deaths (3.2 per 100 person-years) among the 130,496 people who didn't take the pills.

People under age 50 who took the drug faced a greater increase in risk of death than older patients, according to the study,  published in the letters section of JAMA, the Journal of the American Medical Association.

"The benefits of quinine in reducing cramps should be balanced against the risks," the authors wrote.

Patel, who was not involved in the study, said patients who drink beverages with quinine – such as bitter lemon or tonic water – aren't likely getting as much as the patients in the study who took the pills. 

The FDA only allows 83 milligrams of quinine per liter bottle of tonic or quinine water. That comes out to be about 20 milligrams of quinine per 8-ounce glass.

"You'd have to drink over a liter a day to consume 100 milligrams of quinine," she said.

People with leg cramps should still consult their doctor before self-medicating with quinine-laced beverages or any other form of quinine, especially heart patients.

"It's a common complaint, but it's not a good idea to start treating yourself by taking quinine," she said.

Also, leg muscle cramps may be a sign of other health issues, so it's important to get a full work-up to figure out why the cramps are happening.

"It's very rare that patients have isolated muscle cramps and no other symptoms," Patel said.

A Harvard Medical School article published earlier this year explained that leg cramps are "muscle spasms caused by 'mini-seizures' of motor neurons,'" the nerves that help make muscles contract.

They can occur in people with musculoskeletal problems like flat feet or high arches; metabolic disorders such as diabetes; thyroid issues; vascular problems' side effects from certain medications; or neurological conditions such as Parkinson's. Leg cramps are also sometimes chalked up to dehydration and electrolyte imbalance.

Stretching exercises may ease cramps, and taking a vitamin B complex may also help. Patients can also talk with their doctors about taking a calcium-channel blocker called diltiazem (Cardizem, Dilacor XR), the Harvard article said. But magnesium supplements and gapapentin (Neurontin) aren't likely to help, according to Harvard experts.