Do over-the-counter diet pills work? Read this before heading to the supplement aisle

  • 3 Minutes Read
Sue Heikkinen
Sue Heikkinen, MS, RDN, CDCES, BC-ADM, ACE-PT - Registered Dietitian Nutritionist and Certified Diabetes Care and Education Specialist

Over-the-counter diet pills are big business, but do they actually work, and are they safe? Here's what you need to know about the common ingredients in weight-loss supplements.

Over-the-counter diet pills

Have over-the-counter diet pills gotten your attention?

It's hard to ignore the hype of dramatic claims. Can a pill or supplement really melt fat, build muscle, and suppress your appetite? These weight-loss pill claims are so appealing. Worldwide, people spend an estimated $32 billion on weight-loss supplements in a year. One in three Americans trying to lose weight has taken a weight-loss supplement.

Unfortunately, the hype lacks the evidence to back up the claims. Authors of a comprehensive review published in the journal Obesity concluded there is no high-quality evidence that weight loss supplements work.

The truth about supplement regulation and safety

Although a "natural" claim holds great appeal, it does not guarantee safety. Unfortunately, the US Food and Drug Administration does not require supplement manufacturers to prove that their products are safe or work. Although supplement manufacturers cannot claim their products can cure, treat, or prevent any disease, they still promote their products in misleading ways. They often use testimonials or dramatic "before" and "after" pictures without explaining the data or path to the results.

When buying a supplement, you can't be certain of what you are getting. Plenty of reports show supplements containing ingredients not disclosed on the label or containing significantly higher or lower amounts of the "active" ingredient than stated.

Tell your doctor if you use or are considering using a weight-loss dietary supplement (or any supplement, for that matter). Over-the-counter diet pills may interact with your medications or may not be safe for certain medical conditions.

What you need to know about common OTC weight-loss supplement ingredients

Green tea

What is it? Green tea, a tea made from unfermented tea leaves, is consumed as a beverage or supplement in powdered or extract form. Green tea contains caffeine and a flavonoid called EGCG, both of which have potential weight-loss effects.

Is it generally safe? Yes, though consuming large amounts of green tea may cause side effects related to excess caffeine, such as difficulty sleeping, headache, or irregular heartbeat. In addition, green tea extract contains a chemical linked with liver injury.

Will it help me lose weight? Possibly, but any weight loss would be minor. However, unsweetened green tea makes an excellent alternative to high-calorie sweetened beverages.


What are they? Probiotics are bacteria and yeast that survive the digestive process and may have potential health benefits. Probiotics are found in certain fermented foods, such as yogurt, as well as in dietary supplements. Probiotics may affect how we digest and absorb food, and burn calories.

Are they generally safe? Yes, probiotics seem to be safe for most healthy adults.

Will they help me lose weight? Probably not. Despite some promising studies in mice, human study results are inconsistent.

Ma huang/ephedra

What is it? Ephedra, also known as ma huang, is an herb with stimulant properties. It can decrease appetite and speed metabolism. The US Food and Drug Administration banned the sale of ephedra in 1994 due to risks of severe side effects and risk of death.

Is it generally safe? No. Ephedra has significant negative side effects, including high blood pressure, irregular heartbeat, and increased heart attack and stroke risk.

Will it help me lose weight? Perhaps, but it is not worth the risk to your health.


What is it? A tropical fruit, Garcinia cambogia contains the compound hydroxycitric acid (HCA) in its pulp and rind. Possible benefits of HCA include decreased appetite and decreased fat storage.

Is it generally safe? Not enough reliable information exists to know if garcinia is safe. Liver problems were reported by some people taking this product. Still, it is uncertain if these issues were due to garcinia alone. Nausea, stomach discomfort, and headache are potential side effects.

Will it help me lose weight? Not enough evidence exists to prove that garcinia will help with weight loss.

Conjugated linoleic acid (CLA)

What is it? CLA is a fatty acid found naturally in dairy products and meat and in higher concentrations as a supplement.

Is it generally safe? When obtained through food sources, CLA is safe, and possibly safe when taken as a supplement. However, it may cause side effects such as stomach upset, diarrhea, nausea, fatigue, and headache.

Will it help me lose weight? Maybe. CLA might help decrease body fat and reduce hunger, but it doesn't seem to reduce body weight significantly.

Orlistat (alliĀ®)

What is it? Orlistat, sold under the brand name Alli, is the only FDA-approved over-the-counter, weight-loss supplement. It is also available in prescription strength, as the brand Xenical. Alli blocks the absorption of about 25% of the fat you eat.

Does it work? Yes, but don't expect drastic results. Orlistat can promote slightly more weight loss compared to diet and exercise alone. Users can expect to lose an extra pound for every two pounds they lose on their own.

Is it generally safe? Yes, though orlistat reduces the absorption of the fat-soluble vitamins A, D, E, and K. Users must take these vitamins to prevent deficiency. In addition, orlistat can cause unpleasant digestive side effects such as diarrhea and oily stools, especially if the user consumes a high-fat die

Should I take weight-loss supplements or over-the-counter diet pills?

As expected, "sounds too good to be true" claims of weight loss without changing your diet or exercising are false. The potential health risks and lack of weight-loss evidence from unregulated over-the-counter diet pills and supplements suggest you would be better off using the money on a new pair of walking shoes or some fresh produce instead.

If you want to lose a significant amount of weight, you may ask your doctor if prescription weight-loss medication is an option. These medications can also have side effects, but the FDA regulates them for purity and safety, and a health care provider monitors their use. Of course, any weight loss is more effective when combined with lifestyle changes.

References and reliable resources for dietary supplements:

Natural Medicines Database (subscription only)
ConsumerLab (subscription only)
Dietary Supplements for Weight Loss Consumer information from the National Institutes of Health Office of Dietary Supplements

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Apr 25, 2022

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