Methamphetamine addicts who took an antidepressant medication every day were far less dependent on the drug after three months than those who took a placebo, according to a study released Monday by the San Francisco Public Health Department.

Addiction treatment experts said the findings were encouraging, especially given how notoriously difficult it can be to help methamphetamine addicts kick their dependence. But they added that the results will need to be confirmed in larger studies.

Researchers have for years been trying to find a drug to help alleviate dependency on methamphetamine, much as methadone can be used to help people quit heroin, but multiple studies of many different drugs have failed. Addiction experts said they’re cautiously optimistic that the antidepressant mirtazapine, sold under the brand name Remeron, will prove useful.

“This is exciting to see because with methamphetamine, virtually everything we’ve tried hasn’t worked. There have been quite a few bombs pharmacologically,” said Keith Humphreys, a Stanford psychiatry professor and a researcher at the Veterans Administration in Palo Alto who specializes in addiction. “At the same time, those earlier experiences have taught me to be cautious now.”

Addiction on the rise

More than 1 million people in the United States use methamphetamine every year, and the nation has seen a resurgence in addiction to the drug in recent years, according to the National Institute on Drug Abuse. In San Francisco, among people who seek treatment for drug dependence, about 11 percent are abusing methamphetamine, according to the health department.

The study, results of which were published in the Archives of General Psychiatry, was run by Dr. Grant Colfax, director of HIV prevention at the Public Health Department. His interest in treating methamphetamine addiction stems from the close connection between abuse of the drug and exposure to HIV infection.

Effects of methamphetamine include lowered inhibitions and increased feelings of invulnerability, which in turn can lead to risky sex behaviors like having unprotected sex or sex with multiple partners. Regular use of methamphetamines among men who have sex with men can double the risk of HIV infection, Colfax said.

With that in mind, Colfax said he was pleased that the results of his study showed participants who were given mirtazapine not only had lower rates of methamphetamine dependence, but also reported fewer risky sexual behaviors than their peers in the placebo group.

“Methamphetamine treatment for gay men is HIV prevention as well,” Colfax said. “We had dramatic reductions in most risk behaviors.”

The study enrolled 60 participants, all male methamphetamine addicts who regularly have sex with men. Half of the men were given a daily dose of mirtazapine, and half were given a placebo. The men underwent weekly urine tests to check for methamphetamine, and they all had weekly addiction counseling.

Among those who took the antidepressant, the number of positive urine tests fell 40 percent, from 73 percent in the first week of the study to 44 percent in the last week. In the placebo group, positive tests fell just 6 percent, from 67 percent to 63 percent.

Colfax pointed out that adherence to the drug in both the placebo and the mirtazapine group wasn’t great – participants generally took fewer than half of the prescribed doses. That’s not unusual for methamphetamine addicts, who often have trouble following strict treatment protocols. But the fact that dependence was significantly reduced is a good sign anyway, Colfax said.

Treatment for methamphetamine addiction typically includes group or one-on-one counseling sessions, along with a 12-step program similar to Alcoholics Anonymous. Because of the complicated way that methamphetamine interacts with the brain, finding a drug to offset the effects of withdrawal and help people quit has proved elusive.

Opiates, including heroin, aren’t as difficult to counteract, said Gantt Galloway, senior scientist with the Addiction and Pharmacology Research Laboratory at California Pacific Medical Center. But methamphetamine is a “complex drug that has a myriad of effects on the brain,” he said.

‘Promising finding’

An antidepressant like mirtazapine may work because it targets areas of the brain related to drug cravings and reward, addiction experts said. Galloway, who is starting a study of his own looking at the drug Provigil to offset some effects of methamphetamine withdrawal, said the antidepressant study “is a promising finding that certainly needs follow-up.”

“This is absolutely justification for doing a large trial,” Galloway said, “and potentially moving us forward to having an actual treatment.”