A good diet pill—one that is safe and effective—has never been developed. So it was big news when the Food and Drug Administration (FDA) approved not just one prescription weight-loss drug last year, but two—the first ones in 13 years (during which time three diet drugs were taken off the U.S. market.) Both are indicated only for obese people, or for overweight people who have at least one weight-related health condition such as high cholesterol or diabetes. And both are supposed to be used along with diet and exercise.
Belviq. Its active ingredient, lorcaserin, activates a brain receptor for serotonin, which is involved in appetite regulation. In three studies, people who took it for a year lost three to four percent more weight, on average, than those taking a placebo. But Belviq has a long list of cautions and contraindications: It may cause agitation, euphoria, hallucinations, uncontrolled muscle spasms, changes in heart rate and blood pressure, suicidal thoughts and priapism (a painful erection that lasts for hours and needs urgent medical attention), along with more common side effects such as headache, dry mouth, dizziness, nausea and fatigue.
Qsymia (kyoo-SIM-ee-uh). This is a combination of two old drugs: phentermine (a stimulant that suppresses appetite) and topiramate (an epilepsy and migraine drug that supposedly increases fullness and calorie burning and makes food less appealing). In two trials, Qsymia taken for a year resulted in seven to nine percent greater weight loss, on average, than a placebo. That’s twice as much as Belviq, but for obese people, this may still fall short of their weight-loss goals.
Phentermine was the "phen" in the infamous "phen-fen," which was discontinued in 1997 because it caused heart valve problems; it's thought that phentermine alone rarely has this effect. However, the drug is still dangerous. Notably, it can cause spikes in heart rate. It also increases the risk of kidney stones, glaucoma, metabolic acidosis and low blood sugar. Topiramate can have negative effects on mood and has been linked to memory and concentration problems.
Of major concern is the risk for birth defects, which is why Qsymia can be sold only through specially certified pharmacies under what’s called REMS (Risk Evaluation and Mitigation Strategy). This requires that extra steps be taken to ensure that prescribers and patients are fully informed. More common side effects include dry mouth, constipation, insomnia, altered taste and tingling in the fingers and toes.
Our take—don't take
We can't recommend either drug until there is much more experience with them. Their potential risks outweigh their modest benefits. There's also some evidence that they lose effectiveness after the first year. After initially rejecting both drugs for safety reasons, the FDA reversed course because of the urgent need for new treatments for obesity. But that doesn’t mean you should be a guinea pig. In fact, the FDA is requiring further studies of both drugs to determine if they increase the long-term risk of heart disease or stroke. And there is still a lingering concern about heart valve problems.
In any case, many people shouldn’t take the drugs because of medical conditions that preclude their use, such as heart disease, history of stroke, or glaucoma or because the drugs can interact with many medications. Pregnant women should also avoid them.
Critics predict it won’t be long before these drugs are withdrawn from the market. There’s still hope that at least one of the 200-plus diet compounds in development will be a better solution—fingers crossed. Until then, it’s best to stay away from diet pills. If you are very obese and have failed at all other weight-loss attempts, you could talk to your health care provider to see if you are a candidate for surgical intervention (bariatric surgery). It’s not risk-free, either, but its benefits, especially long term, are better proven.