A drug that safely melts the pounds away would be a dream come true, but our analysis shows that the prescription weight loss pill Contrave is not that miracle drug.

In three clinical trials, people who took Contrave up to 56 weeks lost only five to nine pounds more on average than those who took a placebo. And Contrave can cause serious side effects, such as liver damage, seizures, and possible heart risks. That's why Consumer Reports' medical advisers say most people should skip it: such a small amount of weight loss is not worth the risk of those possible side effects.

Contrave is actually two older drugs, combined: the antidepressant bupropion (Wellbutrin and generic), and the addiction-treatment drug, naltrexone (ReVia and generic). We took a closer look at Contrave because as part of our Consumer Reports Best Buy Drugs program, we routinely review the safety and efficacy of weight-loss drugs, and wanted to check how well Contrave measured up on both of those—or didn't.

To do that, we worked with two drug safety experts—Steven Woloshin, M.D., and Lisa M. Schwartz, M.D., both at Dartmouth College’s Geisel School of Medicine and the Institute for Health Policy and Clinical Practice—to review the studies Contrave’s manufacturer, Orexigen Therapetutics, used to gain approval of the drug from the Food and Drug Administration. From there, they developed a Drug Facts Box for Contrave (PDF), which is a consumer-friendly "translation" of the drug's FDA-aproved drug label. Here's what they found:

The FDA approved Contrave in late 2014 to be used along with a reduced-calorie diet and exercise, in those people who are either obese or who are overweight and have another serious condition, such as heart disease, high blood pressure, high cholesterol, or type 2 diabetes. The Contrave drug label—the FDA-approved information about the drug—defines obese as having a body mass index (BMI) of 30 or greater; and being overweight as having a BMI of 27 to 29.9. (BMI is a measure of weight in relation to height and you can calculate yours here.)

Modest Benefits

One of the largest clinical trials to date of Contrave shows obese and overweight people who took the drug for up to 56 weeks lost an average of 12 pounds (or about 5 percent of their body weight), compared with an average of 3 pounds (or 1 percent of their body weight) among those who took a placebo. Both groups were also put on a reduced calorie diet, exercised, and received behavioral counseling.

To put that into perspective, we estimated that a person weighing 220 pounds who takes Contrave for a year could expect to lose about 12 pounds total: 9 pounds from the drug itself and 3 pounds from diet and exercise.  

In another study, obese and overweight people who took Contrave for up to a year shed an average of 18 pounds (or 8 percent of their body weight) while the placebo group lost 11 pounds (5 percent of their body weight). Both groups were also put on a reduced calorie diet, exercised, and received behavioral counseling. The result is that Contrave contributed to losing an additional 7 pounds.

And the findings were even less impressive for people who had diabetes. Overweight people with that disorder who took Contrave for up to a year dropped an average of 9 pounds or 4 percent of their body weight, while those who took a placebo lost 4 pounds, or 2 percent of their body weight. In that case, Contrave helped people lose only 5 additional pounds.

Also, not everyone who takes Contrave will experience meaningful weight loss: In one trial, about 42 percent of people who took Contrave lost 5 percent or more of their weight compared to 17 percent of those who took a placebo.

Serious Risks

“The studies show that Contrave caused many people to feel sick,” says Schwartz. Nearly 1 in 4 people in the clinical trials stopped taking the prescription weight loss pill because they couldn’t tolerate the common side effects, including nausea, headache, and vomiting.

Contrave can also cause increased blood pressure, anxiety, and insomnia. Other side effects include constipation and dizziness.

See our Drug Facts Box (PDF) for the full analysis of the prescription weight loss pill Contrave.

Like other drugs that contain the antidepressant bupropion, Contrave carries a black-box warning—the strongest type issued by the FDA. Although Contrave is not intended for those under the age of 18, the warning states that the drug can, in rare instances, increase suicidal thoughts and behaviors in adolescents and young adults. It could also cause mania and depression to return in people who have previously suffered from those conditions. Other rare but serious side effects include seizures and a condition where eye pressure rises rapidly (angle-closure glaucoma).

The FDA was particularly concerned that Contrave might also raise the risk of heart problems, such as heart attack and stroke, so it required the manufacturer, Orexigen, to conduct a clinical trial to figure out if the drug is safe for the heart. But Orexigen has started and stopped two heart trials before they were finished. Now, the company says it plans to launch a third trial, but the results aren’t expected to be available until 2021.

In the meantime, the FDA still approved the drug without requiring the trial be completed, so Contrave remains available in the U.S. while its effect on the heart is still being investigated.

In a statement to Consumer Reports, Orexigen Therapeutics, said preliminary data from its first heart risk trial “provide valuable information and support our confidence in the overall safety for Contrave.”

However, the FDA told us that Contrave's heart risks remain unknown. Eric Pahon, a spokesman for the FDA, said it was premature to draw any conclusions from Contrave's first heart trial, so determining whether Contrave poses a risk to the heart will require completing the new study.

Steven Nissen, M.D., chair of Cardiovascular Medicine at the Cleveland Clinic, who led one of the trials, agrees with the FDA. “We don’t have a definitive answer about the safety of this drug and we won’t have one for a very long time,” he says.

Bottom Line

We’ve previously advised against the use of weight loss medications, such as Alli or Xenical, Belviq, Qsymia, and Saxenda—and now Contrave joins that list—because they don’t help most people lose much, if any, weight, and they all carry potentially serious risks. For most people, the limited benefit of Contrave isn’t worth the risk of side effects or unknown heart risks, so our medical advisers recommend skipping it.

To be sure, our analysis suggests that Contrave can help people lose a meaningful amount of weight, if they are able to tolerate it and stick with an exercise and reduced-calorie diet over the course of a year. But they would also expose themselves to the serious risks of the drug. Instead, CR medical advisers say lose weight the safer way—by eating less and exercising.

If you've been unable to lose weight on your own, ask your doctor about intensive behavioral programs that have at least 12 sessions a year and include multiple strategies to help you switch to healthier diets and increase physical activity. Such programs can lead to an average weight loss of 9 to 15 pounds (or 6 percent of body weight) in the first year, according to the U.S. Preventive Services Task Force.

Also good to know: If you still decide to try Contrave, and haven’t dropped at least 5 percent of your weight after three months of taking the drug at the target dose, you should stop taking it because it’s unlikely that you ever will, according to information on Contrave's drug label.

See our advice on what really works for weight loss, including our Ratings of diet plans.

Editor's Note: This article and related materials are made possible by a grant from the state Attorney General Consumer and Prescriber Education Grant Program, which is funded by the multistate settlement of consumer-fraud claims regarding the marketing of the prescription drug Neurontin (gabapentin).