According to the Centers for Disease Control and prevention (CDC), methamphetamine use is increasing in many parts of the United States. The stimulant is very addictive, it can be injected, and it can increase sexual arousal while reducing inhibitions. Because of these qualities, public health officials are concerned that users may be putting themselves at increased risk of acquiring or transmitting HIV infection. A new UCLA study has found that Naltrexone, which is used to treat alcoholism, significantly reduced user’s craving for methamphetamine, and that it made them less aroused by the drug. The study was published in the journal Neuropsychopharmacology and is the first in the United States to evaluate Naltrexone for treating methamphetamine addiction.
“The results were about as good as you could hope for,” explained lead author Lara Ray, PhD, a UCLA associate professor of psychology and director of the UCLA Addictions Laboratory. Dr. Ray and her colleagues evaluated 22 men and 8 women who use methamphetamine an average of three to four days a week. The subjects were hospitalized for four days. During that period, each subject was given either Naltrexone (25 milligrams the first two days, and 50 milligrams on days three and four) or a placebo daily. Ten days later, the subjects were readmitted to the hospital for four more days/ The treatment groups were reversed; those that previously received Naltrexone were given placebos, and those that previously received the placebo were given Naltrexone.
On the last day of each hospital visit, all subjects were given intravenous doses of methamphetamine. Three hours later, they were asked how they felt and how much they wanted more of the drug. The investigators found that Naltrexone significantly reduced the subjects’ craving for methamphetamine; furthermore, it made them less aroused by methamphetamine than in the past. Their heart rates and pulse readings both were significantly higher when they were given the placebo than when they took Naltrexone. In addition, participants taking Naltrexone had lower heart rates and pulses when they were presented with their drug paraphernalia than those who were given placebos.
Dr. Ray explained that the study revealed that Naltrexone reduced the rewarding effects of the drug; those taking Naltrexone did not find methamphetamine to be as pleasurable and were much less likely to desire more of it. Naltrexone was well tolerated and had minimal side-effects. Both men and women both were helped by taking Naltrexone; however, the positive effect on men was slightly less. It made no difference whether the participants were given Naltrexone during their first hospital stay or their second.
Naltrexone acts by blocking opioid receptors in the brain. Previous studies of individuals undergoing treatment for alcoholism reported that the subjects achieved less of a “high” from drinking when they take Naltrexone. The researchers next plan to examine whether Naltrexone would be more effective in combination with other medications and at different doses.
