At 3 am, infomercials claiming weight loss by pill-popping with testimonials from beautiful, model-like “real people” can be incredibly persuasive. Diet pills may be ever-present, but with unwelcome side effects and serious health risks, are they safe?

Not So Smart Drugs — Why It Matters

potentially dangerous compounds without including the information on their labelsAdverse drug reactions of a slimming product contaminated with sibutramine. Van Hunsel, F., van Grootheest, K. Nederlands Bijwerkingen Centrum Lareb, Hertogenbosch, the Netherlands. Netherlands Journal of Medicine, 2011;155(42):A3695..

Research has found undeclared prescription drugs, banned drugs, and illicit agents in numerous commercial diet pills (yikes!), so it’s possible for these pills to not only deviate from the label’s claims, but also cause unwanted side effects and health risksCase series on a diversity of illicit weight-reducing agents: from the well known to the unexpected.Tang, M.H., Chen, S.P., Ng, S.W., et al. Hospital Authority Toxicology Reference Laboratory, Block P, Princess Margaret Hospital, Laichikok, Hong Kong, China. British Journal of Clinical Pharmacology, 2011 Feb;71(2):250-3.. The scariest part? Many of these products are easily available from pharmacies, drug stores, or online!

Yes, some diet pills do what they claim. Orlistat, the only FDA approved drug for long-term weight loss (sold as Xenical by prescription and over the counter as Alli), works by blocking fat absorption and has been found to boost weight loss by up to 50 percent (…when added to a reduced calorie, lower-fat diet, that is)Over-the-counter weight loss with orlistat? Evidence Based Nursing, 2010 Jul;13(3):98-100.. While long-term side effects are unknown (the drug was only approved in 1999), the short-term side effects are almost too icky to mention — involuntary fecal discharge, anyone? (Read: you can poop your pants at any time.) Phentermine, approved by the FDA for short-term weight loss, helps drop pounds (when paired with increased physical activity and a reduced calorie diet) by suppressing appetitePhentermine, topiramate and their combination for the treatment of adiposopathy (‘sick fat’) and metabolic disease. Bays, H. L-MARC Research Center, 3288 Illinois Avenue, Louisville, KY USA. Expert Review of Cardiovascular Therapy, 2010 Dec;8(12):1777-801.. But, of course, there is more to weight loss than appetite, and the side effects of this drug include increased blood pressure, dizziness, sleeplessness, nervousness, and constipationSatiety and body weight control. Promise and compromise. Comment on ‘Satiety. No way to slim.’ Bellisle, F., Tremblay, A. Division of Kinesiology, PEPS, Laval University, Québec, Canada. Appetite, 2011 Dec;57(3):769-71;discussion 784-90.RE: Pulmonary Hypertension Associated with Use of Phentermine. Hendricks, E.J., Rothman, R.B. Yonsei University College of Medicine. Yonsei Medical Journal, 2011 Sep;52(5):869-70..

Even though these diet drugs do completely different things, they share one key ingredient — a lower calorie diet. So are the drugs causing the weight loss, or is healthy eating doing a lot of the work? Hmm…

A Bitter Pill — The Answer/Debate

Easily purchased with a click of the mouse, with bathing-suit season just around the corner, diet-pills can be pretty tempting for the nutritional over-achievers out there. But with only a limited number of FDA sanctioned weight loss drugs, many diet pills on the market may only lighten the wallet. Others are getting the smack down from the FDA as being dangerous due to ingredients like bitter orange, Sibutramine, and Hoodia, which can cause side effects ranging from high blood pressure and liver or heart problems, to headaches, nausea, and shortness of breathAdulteration of over-the-counter slimming products with pharmaceutical analogue — an emerging threat. Yuen, Y.P., Lai, C.K., Poon, W.T., et al. Department of Pathology, Princess Margaret Hospital, Laichikok, Kowloon, Hong Kong. Hong Kong Medical Journal, 2007 Jun;13(3):216-20.Consumption of dietary supplements containing Citrus aurantium (bitter orange)–2004 California Behavioral Risk Factor Surveillance Survey (BRFSS). Klontz, K.C., Timbo, .BB., Street, D. Center for Food Safety and Applied Nutrition, Food and Drug Administration, College Park, MD USA. Annals of Pharmacotherapy. 2006 Oct;40(10):1747-51.Anti-Obesity Drugs: A Review about Their Effects and Safety. Kang, J.G., Park, C.Y. Department of Endocrinology and Metabolism, Hallym University Sacred Heart Hospital, Hallym University School of Medicine, Anyang, Korea. Diabetes Metabolism Journal. 2012 Feb;36(1):13-25.Effects of 15-d repeated consumption of Hoodia gordonii purified extract on safety, ad libitum energy intake, and body weight in healthy, overweight women: a randomized controlled trial. Blom, W.A., Abrahamse, S.L., Bradford, R., et al. Unilever Research & Development, Vlaardingen, Netherlands. American Journal of Clinical Nutrition. 2011 Nov;94(5):1171-81..

Still thinking about trying diet pills? Be sure to read the labels and do the research on safety alerts and recalls. But most of all, talk with a pharmacist or doctor so health status and current medications can be taken into account. Just remember: When it comes to weight loss, there is no magic bullet, pill, or potion — the best answer is always diet and exercise.

This article has been read and expert verified by Sherry Pagoto and Jessica Redmond.

The Takeaway

  • Unlike the tests drugs must go through before being approved, diet pills are considered “dietary supplements” and do not have such stringent standards to land on store shelves.
  • Research has found undeclared prescription drugs, banned drugs, and illicit agents in numerous commercial diet pills (yikes!), so it’s possible for these pills to not only deviate from the label’s claims, but also cause unwanted side effects.
  • While it’s important to be very careful, some approved diet pills can work as they claim, though positive results are most often achieved when paired with improved diet and regular exercise.
  • Before using any diet or weight-loss pill, it’s essential to speak with a doctor!