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 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 contended.
The Lancet findings echo those of studies into other diet drugs such as 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."
An accompanying Lancet editorial noted that one concern is that blood pressure did not drop as much as expected in the higher weight-loss group. "More data are needed to get a better overall assessment of cardiovascular risk of this otherwise promis
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