FRIDAY, July 30 (HealthDay News) -- Contrave, an experimental weight loss drug that combines an antidepressant with an anti-addiction medication, appears to help users shed pounds when taken along with a healthy diet and exercise, researchers report.

People who took the drug for more than a year lost an average of 5 percent or more of body weight, depending on the dose used, the team said.

However, the regimen did come with side effects, and about half of study participants dropped out before completing a year of treatment.

Contrave is combination of two well-known drugs, naltrexone (Revia, used to fight addictions) and the antidepressant bupropion (known by a number of names, including Wellbutrin). The drug, which is up for U.S. Food and Drug Administration review this December, appears to boost weight loss by changing the workings of the body's central nervous system, the researchers report.

The researchers, who report their findings online July 29 in The Lancet, enrolled men (15 percent) and women (85 percent) from around the country, ranging in age from 18 to 65. They were all either obese or overweight with high blood fat levels or high blood pressure.

The participants were told to eat less and exercise, and they were randomly assigned to take a twice-daily placebo or a combination of the two drugs with naltrexone at one of two levels.

After 56 weeks, only about half (870) of the more than 1,700 participants initially enrolled remained in the study. Almost half (48 percent) of those who took the highest dose of naltrexone lost 5 percent of their weight or more, while only 16 percent of those who took placebos did.

However, about 30 percent of those taking Contrave experienced nausea, the study authors say, and other side effects included headache, constipation, dizziness, vomiting and dry mouth.

Still, Contrave may give people struggling to lose weight a new option, the researchers contend. "Although lifestyle modification is first-line therapy for obesity, adherence to this intervention is poor," they write. "The combination of naltrexone plus bupropion could be a useful addition to the current range of medications that facilitate adherence to lifestyle modification and produce clinically meaningful weight loss for treatment of obesity and obesity-related disorders."

The findings reflect the results of studies into other drugs, such as the diet drugs Meridia, Xenical and Alli, said Lona Sandon, an assistant professor of clinical nutrition at the University of Texas Southwestern Medical Center in Dallas and spokeswoman for the American Dietetic Association.

"When these are combined with a modestly reduced calorie diet, modest amounts of weight loss are achieved," she said. "One striking thing to note is the study drop-out rate of 50 percent. This may have been due to side effects of medications, the fact that it is hard to stick to dietary changes for 56 weeks, or [the fact that] slow and only modest weight loss did not meet participant expectations."

Cynthia Sass, a New York City-based nutritionist and author, added that drugs used to treat addiction also appear to help with weight control, supporting "the notion that food can be addictive for many people."

The authors noted that additional studies are needed before putting this regimen into practice. One concern is that blood pressure did not drop as much as expected in the higher weight-loss group, an accompanying editorial notes. "More data are needed to get a better overall assessment of cardiovascular risk of this otherwise promising combination therapy for obesity," wrote Professor Arne Astrup, a nutrition expert at the University of Copenhagen, Denmark.

More information

For more about weight loss, visit the U.S. National Library of Medicine.