DR. MOHLER: Diet drugs — 2 new ones on the market but don’t get too excited

Phil Mohler, M.D.
Free Press Health Columnist

In the last few months, the FDA has approved two new weight loss drugs. These are the first diet drugs approved in 13 years, during which time three diet drugs were taken off the U.S. market. Both of these drugs are indicated only for obese people, or for overweight people who have another weight-related health problem like diabetes or high cholesterol.

Belviq activates an appetite receptor in the brain and works by making patients feel full, so they eat less.

• Three clinical studies showed that people who took it for a year, lost 3–4% of their weight. A 200-pound patient would drop a not very impressive 6-8 pounds in a year.

• Belviq may cause low blood sugar, headache, fatigue, agitation, dizziness, dry mouth and painful erections; it has negative interactions with some antidepressants, cough medicines with dextromeththorphan, and St. John’s Wort.

• Belviq is pricey at around $200/month.

Qsymia is a combination of two old drugs: phentermine, the “phen” in phen-fen that was taken off the market in 1997 because of heart valve problems; and topiramate, a migraine and epilepsy drug that reportedly creates a sense of fullness.

• In two trials, patients who took Qsymia for a year lost 7-9% of their weight. That’s twice as much as Belviq.

• Phentermine’s heart valve effects are quite rare, but it may cause spikes in heart rate; topiramate may cause kidney stones, increased pressure in the eyes, low blood sugar and depression.

• Phentermine has been associated with birth defects in animals. Women of childbearing age must have a negative pregnancy test prior to starting Qsymia and then monthly pregnancy tests.


• The potential risks for both these drugs far outweigh their modest benefits.

• Remember that many new drugs are brought to market having been tested on as few as 1,500 patients. If a serious adverse event occurs in one out of 2,000 patients taking the drug, the studies will not identify it! Recall Sir William Osler’s tongue in cheek advice, “Use new drugs while they are still safe.“

• The current solution to weight reduction is not in a pill bottle. Losing weight involves watching what we put in our mouths and exercising regularly.

• I predict that both Belviq and Qsymia will be removed from the market because of their side effects in the next two years.

Dr. Mohler has practiced family medicine in Grand Junction for 38 years. He has a particular interest in pharmaceutical education. Phil works part-time for both Primary Care Partners and Rocky Mountain Health Plans. Email him at

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