With few effective nonsurgical options for treating obesity, doctors often prescribe combinations of existing drugs to try to boost weight loss. Problem is, if those combos haven’t been adequately studied, you don’t know how well they work—or what the risks really may be.
"You have to worry about the side effects of each drug and then the new side effects that may result from the combination," Dr. Kaplan notes. Here's the truth about three common combinations.
Combines the appetite suppressant phentermine with topiramate, an anti-convulsant prescribed under the name Topamax to treat epilepsy and migraines.
In clinical trials, patients taking the highest dose of Qnexa, a drug that uses this duo, lost nearly 9% more weight than those taking a placebo. But because of concerns about the potential for birth defects and heart problems, the FDA decided late last year not to approve the drug.
Marries bupropion, an antidepressant also known as Wellbutrin, and naltrexone, an opioid blocker used to treat alcohol and narcotic addiction. This pairing is found in the drug Contrave, which the FDA also recently declined to approve.
In clinical trials, people taking Contrave lost an average of only 4.2% more weight than those taking a placebo, which is shy of the FDA’s standard of 5%. The FDA also said the drug’s maker needs to do a long-term study to show that Contrave doesn’t raise the risk of heart attack.
Combines phentermine with 5-HTP—short for 5-hydroxytryptophan, an over-the-counter supplement used as an antidepressant, appetite suppressant, and sleep aid—and carbidopa, used to treat Parkinson’s disease. A 2009 study found that 20% of physician members of the ASBP who responded to a survey prescribe the combo as a weight-loss treatment even though it’s never been studied in a clinical trial.
While there are no controlled studies reporting on the risks of this combo, possible side effects of phentermine include heart palpitations and increased blood pressure, and taking 5-HTP with carbidopa may cause thickening and inflammation of the skin.