The temptation to use over-the-counter weight-loss pills to lose weight fast is strong. But are these products safe and effective?

By Mayo Clinic Staff

The appeal of losing weight quickly is hard to resist. But do weight-loss pills and products lighten anything but your wallet? And are they a safe option for weight loss? Here's a look at some over-the-counter weight-loss pills and what they will and won't do for you.

There's no magic bullet for losing weight. The most effective way to lose weight and keep it off is through lifestyle changes. Eat a healthy low-calorie diet with lots of fruits and vegetables and be physically active.

Weight-loss pills — prescription medicines, nonprescription drugs, herbal medicines or other dietary supplements — are all, at best, tools that may help with weight loss. But there is relatively little research about these products, and the best studied of these are prescription weight-loss drugs.

For example, a 2014 study reviewed 21 long-term trials of prescription drugs for treating obesity. The researchers concluded that when a person makes appropriate lifestyle changes, a prescription weight-loss drug increases the likelihood of achieving "clinically meaningful" weight loss within a year.

Clinically meaningful weight loss — enough weight loss to begin lowering the risk of cardiovascular disease, diabetes and other diseases — is generally defined as 5 percent or more of body weight.

It's important to consider, however, that weight loss achieved in a research setting may be greater than in actual practice. Also, possible side effects and adverse reactions to weight-loss pills can affect the treatment outcome.

A reasonable expectation, therefore, is that prescription weight-loss pills may be beneficial, but they won't be magical. They do not work for everyone, and their benefit may be modest. And researchers know much less about the potential benefits and risks of over-the-counter weight-loss products.

Over-the-counter weight-loss treatments fall into two general categories:

  • Nonprescription drugs
  • Dietary supplements

The standards for regulating the production and marketing of these two types of treatments are different. For a nonprescription drug, such as orlistat (Alli), the drug company must provide the Food and Drug Administration (FDA) with results from human (clinical) trials that show the safety and effectiveness of the drug at the nonprescription dose.

The maker of a dietary supplement is responsible for ensuring the safety of a product and making honest claims about possible benefits. However, the maker's claims are not subject to FDA review or approval before marketing. Also, the type or quality of research used to support claims can vary.

If the FDA can demonstrate that a substance is unsafe, the agency can ban the product or ask a manufacturer to withdraw it voluntarily. The FDA may also take action against a manufacturer if there is no evidence at all to support a claim.

These differences in research, production and marketing can make it difficult for people to make informed decisions about products.

When a dietary supplement is marketed as "clinically proven" to cause weight loss, there should be some type of clinical evidence to support it. Such a claim, however, provides no details about the clinical research.

For example, raspberry ketone supplements are marketed as clinically proven, natural weight-loss products. As of November 2014, the results of only one clinical trial with raspberry ketone had been published. The results include the following information:

  • The eight-week trial used a multi-ingredient supplement with raspberry ketone, caffeine, bitter orange, ginger root extract and garlic root extract, as well as other herbs, vitamins and minerals.
  • Seventy obese adults were randomly assigned to receive either the supplement or an inactive ingredient (placebo).
  • All of the participants were placed on a restricted diet and exercise program.
  • Forty-five people completed all eight weeks of the trial.
  • Among people completing the trial, the average weight loss in the supplement group was 4.2 pounds (1.9 kilograms).
  • The average weight loss in the placebo group was 0.9 pounds (0.4 kilograms).

While the difference between the two groups was significant, the weight loss in the treatment group was still modest. And the trial was only eight weeks, which is not long enough to know if the supplement will help promote weight loss over the long term. Because the supplement included multiple ingredients, it's not possible to judge which ingredients caused a treatment effect.

Therefore, the size, method and duration of the trial provide insufficient evidence to draw conclusions about the potential benefits of raspberry ketone.

Limited research also makes it difficult to judge the safety of a weight-loss supplement. And a product isn't necessarily safe simply because it's natural.

Ephedra, or ma huang, is an herbal stimulant that was once used in weight-loss products. In 2004, the FDA banned ephedra because of possible adverse effects, including mood changes, hypertension, irregular heart rate, stroke, seizures and heart attacks.

Bitter orange is a currently available herbal stimulant that is often called an "ephedra substitute" and is used in some weight-loss supplements. The active ingredient in bitter orange has chemical properties and actions that are similar to ephedra and may be associated with similar adverse effects. Because of limited research and the use of bitter orange in multi-ingredient supplements, the safety of the product isn't well-understood.

It's important to do your homework if you're thinking about trying over-the-counter weight-loss pills. General information about many dietary supplements is available at the website of the National Center for Complementary and Alternative Medicines.

The Natural Medicines Comprehensive Database summarizes research regarding dietary supplements and herbal products. Although the database is only available by subscription, you may be able to access it through a public library.

The following table shows common weight-loss pills and what the research shows about their effectiveness and safety.

Product Claim Effectiveness Side effects
SOURCES: JAMA, 2014; GLAXOSMITHKLINE CONSUMER HEALTHCARE, 2014; NATIONAL INSTITUTES OF HEALTH OFFICE OF DIETARY SUPPLEMENTS, 2014; NATURAL MEDICINES COMPREHENSIVE DATABASE, 2014; GASTROENTEROLOGY RESEARCH AND PRACTICE, 2011; JOURNAL OF THE INTERNATIONAL SOCIETY OF SPORTS NUTRITION, 2013.
Alli — nonprescription version of orlistat Decreases absorption of dietary fat Modest benefit, less effective than prescription-strength orlistat (Xenical) Loose stools, oily spotting, frequent or hard-to-control bowel movements; reports of rare but serious liver damage
Bitter orange (Citrus aurantium) Increases calories burned, suppresses appetite Possible modest benefit; very little data Increased heart rate and blood pressure; reports of anxiety, stroke, irregular heartbeat, heart attack
Chitosan (from exoskeleton of shellfish) Blocks absorption of dietary fat Probably ineffective; few well-designed studies Uncommon: upset stomach, nausea, gas, increased stool bulk, constipation
Chromium (essential mineral) Increases lean muscle mass, decreases appetite, increases calories burned Probably ineffective Uncommon: watery stools, headache, weakness, insomnia, nausea, vomiting, constipation, dizziness, hives
Conjugated linoleic acid (derived from dairy products and beef) Reduces body fat Possible modest benefit Upset stomach, nausea, constipation, loose stools; may decrease good cholesterol and increase bad cholesterol
Green coffee extract Reduces absorption of sugar (glucose), increases calorie and fat metabolism Possible modest benefit Excessive use: anxiety, agitation, insomnia, nausea, irregular heartbeat
Green tea extract Decreases fat absorption, increases calorie and fat metabolism Possible slight benefit Long-term use with high doses: insomnia, agitation, dizzinesss, nausea, vomiting, bloating, gas, diarrhea; reports of liver damage
Guar gum (derived from Indian cluster bean) Blocks absorption of dietary fat, increases feeling of fullness Probably ineffective Abdominal pain, gas, diarrhea
Hoodia (succulent plant) Decreases appetite Probably ineffective; insufficient data Headache, dizziness, nausea, vomiting; possible increase in heart rate and blood pressure
Raspberry ketone Increases fat metabolism Insufficient data Insufficient data

If you're considering weight-loss pills, be sure to talk with your doctor, especially if you have health problems, take prescription drugs, or are pregnant or breast-feeding. It's important to get advice on possible interactions with your current use of medicine, vitamins or minerals.

Your doctor can offer advice on losing weight, provide support, monitor your progress or refer you to a dietitian.

Dec. 19, 2014