The Truth About Weight-Loss Pills

Medically Reviewed

Taking medication to help you lose weight is an option when diet and exercise don’t work. However, weight loss pills should be used only by people whose body mass index (BMI) exceeds 30 or by those with a BMI of 27 or more who have serious medical conditions that could be improved by weight loss.

Weight-loss pills do not magically melt away pounds. While they may make it easier to follow lifestyle changes by reducing hunger, they do not eliminate the need to alter behavior permanently. For good results, drug therapy must be combined with dietary, exercise and behavior modifications.

Medication is not always effective. For example, people whose excessive eating is triggered by habits, stress or emotions will probably benefit less from weight-loss pills that reduce appetite than those who overeat because of physical hunger. If no weight is lost in the first few weeks of use, the drug is unlikely to help and should be discontinued. But never stop taking a drug without consulting your doctor first.

Weight-loss pills can cause serious reactions when taken with some other kinds of medications, so be sure to tell your doctor about any drugs (prescription, over-the-counter, or recreational), supplements or herbal preparations you take.

Lipase inhibitors and noradrenergics were the first two classes of drugs approved to treat obesity. Four new medications have been approved in recent years; two in 2012, one in 2014 and the fourth, liraglutide (Saxenda), in 2015.

Lipase inhibitors (Xenical, Alli)

Orlistat (Xenical), a lipase inhibitor that is taken with meals, blocks the absorption of dietary fat from the intestine. It doesn’t prevent all the fat in your diet from being absorbed—just a third of it.

Xenical is the only weight-loss pill that blocks the absorption of nutrients (the others work by reducing appetite). Thus, it’s a good option when stress or bad habits are the cause of overeating. Xenical is also a good choice for people who have trouble avoiding high-fat, high-calorie foods. This is because the drug causes unpleasant gastrointestinal symptoms, such as cramping, oily anal leakage and explosive diarrhea, when these fatty foods are eaten.

Because fat absorption is decreased with Xenical, use of the drug can lead to a loss of the fat-soluble vitamins A, D, E and K and beta-carotene in the stools. To ensure that you are getting enough of these vitamins, take a daily multivitamin. Xenical can also affect the body’s ability to absorb the thyroid hormone replacement medication levothyroxine (Synthroid, Levoxyl), which is prescribed for hypothyroidism (underactive thyroid). It is recommended that Xenical and levothyroxine be taken four hours apart. Be sure to tell your doctor if you take levothyroxine.

A half-strength version of Xenical called Alli is available over the counter. Alli blocks absorption of a quarter of the fat in your diet. Studies have shown that dieters who used Alli lost 50 percent more weight than those who followed a weight-loss diet alone. However, that 50 percent advantage is only around 6 pounds on average. Talk to your doctor or pharmacist before taking Alli if you are taking medicine for diabetes or thyroid disease, or if you are taking other weight-loss products.

Xenical and Alli have been found to cause severe liver injury in rare instances, and the Food and Drug Administration added safety information about this to the products’ labels in 2010. People taking the drugs should be aware of the signs of liver injury, which include itching, yellow eyes or skin, dark urine, loss of appetite or light-colored stools. (In 2014, Alli’s manufacturer issued a voluntary recall of all Alli products in response to concerns about sales of a counterfeit version of the drug. The counterfeit version does not contain orlistat; instead, it contains sibutramine, a stimulant. This should only be taken under a doctor’s supervision.)


These weight-loss pills, such as phentermine (Adipex-P, Ionamin) and phendimetrazine (Bontril PDM), increase levels of norepinephrine in the brain. Because norepinephrine reduces appetite through its actions on the central nervous system, noradrenergics are a good option for people who experience a lot of hunger that gets in the way of eating a low-calorie diet. On average, people taking these drugs lose about half a pound more per week than those taking a placebo.

Phentermine is one of the drugs in Qsymia, a combination drug approved by the FDA in 2012 that also includes topiramate, a drug approved for the treatment of seizure disorders and migraines that has been shown to have a significant effect on weight loss.

Noradrenergics can sometimes cause serious side effects, such as increased blood pressure and heart rate, sleeplessness, and nervousness and can be addictive. This is why they’re typically prescribed for only three months at a time. They can be especially dangerous for people with heart disease, high blood pressure, thyroid problems or glaucoma.

Drugs that increase serotonin

Another weight-loss pill approved in 2012 is lorcaserin (Belviq), which activates receptors for the brain chemical serotonin. Serotonin is a neurotransmitter that regulates mood and also acts to control appetite by producing feelings of fullness and satisfaction even if your stomach is not full.

Drugs that increase serotonin activity have been used for years as antidepressant medications and, more recently, to treat obesity. Lorcaserin targets only those serotonin receptors that affect appetite. The most common side effects include headache, dizziness, fatigue, nausea and dry mouth. In patients with diabetes, the lorcaserin can cause low blood sugar.

An earlier drug, sibutramine (Meridia), raises serotonin and norepinephrine levels in the brain. Meridia was approved in 1997, but was taken off the market at the end of 2010 following months of debate over its risks. Some researchers had linked Meridia to heart attacks and strokes. Use of the drug also resulted in a fairly small amount of weight loss. The FDA concluded that the very modest weight loss that people achieved on this drug did not outweigh the risk of heart attack and stroke and requested that it be removed from the market.

Although the FDA has not approved antidepressants for the treatment of obesity, people who are taking antidepressants called selective serotonin reuptake inhibitors (SSRIs)—for example, fluoxetine (Prozac) or sertraline (Zoloft)—often lose weight. Typically, physicians prescribe these drugs for weight loss in people who are also depressed. The SSRIs increase brain levels of serotonin, and some people taking SSRIs feel less hungry, are less concerned with food and are better able to control their appetites. In general, studies of these medications have found that people who use them lose modest amounts of weight for up to six months, but then tend to regain it even if they are still on the drug.

One exception to this is bupropion (Wellbutrin), which works differently than SSRIs. In one study, participants who took Wellbutrin maintained their weight loss for up to one year. As with most other drugs, antidepressants can cause side effects such as dry mouth, insomnia and decreased libido. One of the newest medications for weight management, Contrave, contains bupropion and the anti-addiction drug naltrexone. One benefit of Contrave, which was approved by the FDA in 2014, is that it has no addictive potential.

Antidiabetes drug

Liraglutide (Saxenda), an injectable medication originally designed and used for the treatment of type 2 diabetes, was approved by the FDA in 2015 as a treatment for chronic weight management. Saxenda is a type of drug known as an incretin mimetic. These drugs mimic glucagon-like peptide-1 (GLP-1), a hormone produced in the intestine that tells the brain that you are full. If at least 4 percent of baseline body weight has not been lost after four months, Saxenda should be discontinued as it is unlikely that meaningful weight loss will be achieved with continued use.

In clinical trials, the most common adverse effects reported were nausea and diarrhea. Serious side effects reported include pancreatitis, gallbladder disease, kidney impairment, and suicidal thoughts. Saxenda can also raise heart rate and should be discontinued in patients who experience a sustained increase in resting heart rate Thyroid tumors have been reported in animal studies of liraglutide, but it is unknown whether there is an increased risk in humans.

As a condition of approval, the FDA is requiring a warning about potential thyroid cancer risk on the label and additional study on this and other health risks, including cardiovascular safety.