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The Skinny on Weight Loss Supplements: Fact or Fantasy?

  • Authors: Darrell T. Hulisz, PharmD; Karen M. Lindberg, PharmD
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Target Audience and Goal Statement

This activity is intended for pharmacists, nurses, physicians, nurse practitioners, and physician assistants.

The goal of this activity is to review available dietary supplements that are marketed for weight loss, describing studies that have examined their efficacy and safety, so that clinicians will be able to counsel patients on this topic.

Upon completion of this activity, participants will be able to:

  1. Identify the most commonly used non-prescription products for weight loss
  2. Discuss studies that have examined the efficacy of each product
  3. Describe safety concerns, possible side effects, and potential drug interactions for each product


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  • Darrell T. Hulisz, PharmD

    Associate Professor, Department of Family Medicine, Case Western Reserve University School of Medicine, University Hospitals, Case Medical Center, Cleveland, Ohio


    Disclosure: Darrell T. Hulisz, PharmD, has disclosed that he has received grants for educational activities from Pfizer, Takeda, and Novartis. Dr. Hulisz has also disclosed that he has served as an advisor or consultant for Pfizer, Takeda, and Novartis.

  • Karen M. Lindberg, PharmD

    Staff Pharmacist, Rite Aid Pharmacy, North Canton, Ohio


    Disclosure: Karen M. Lindberg, PharmD, has disclosed no relevant financial relationships.

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The Skinny on Weight Loss Supplements: Fact or Fantasy?


Usnic Acid, White Kidney Bean Extract, Willow Bark, Yohimbine

Usnic Acid

Usnic acid is sometimes found in proprietary blends or multi-ingredient weight loss supplements. However, there is no convincing scientific evidence that it is effective for weight loss, and there have been reports of toxicity.

Two cases of severe hepatotoxicity were reported in previously healthy 38-year-old patients consuming dietary supplements containing usnic acid within the previous 3 months. Fulminant liver failure requiring transplantation developed in 1 patient; submassive hepatic necrosis that did not require transplantation developed in the other patient.[41]

In another case report, fulminant liver failure requiring transplantation developed in a previously-healthy 28-year-old female after she ingested 500 mg usnic acid daily for a total of 18 days in the previous month.[42]

Take-home message. Due to a lack of evidence of efficacy and to the potential for serious adverse reactions, usnic acid should not be recommended for weight loss.

White Kidney Bean Extract (Phaseolus vulgaris)

White kidney bean extract is advertised as a "carb blocker" that reduces the rate at which starch is converted to sugar in the digestive process, thus reducing caloric intake. In an 8-week, double-blind, placebo-controlled phase 2 trial of a supplement containing white kidney bean extract, 50 adults were treated with 1500 mg twice daily or placebo for 8 weeks.[43] Only 27 patients completed the study. The treatment group lost an average of 3.79 pounds while the placebo group lost an average of 1.65 pounds. Triglycerides were decreased threefold in the treatment group compared with the placebo group. Statistical significance was not achieved for either weight loss or triglyceride changes.

In a randomized, double-blinded, placebo-controlled study in 60 overweight volunteers, patients were given Phaseolus vulgaris extract (445 mg daily) or placebo for 30 days before each carbohydrate-rich meal.[44] Outcomes measured were weight, fat, non-fat, skin fold thickness, and waist/hip/thigh circumferences. Subjects in the treatment group had a significant reduction of body weight, BMI, fat mass, adipose tissue thickness, and waist/hip/thigh circumferences. In this study, mean BMI was reduced by 1.0 kg/m over placebo.

Take-home message. White kidney bean extract inhibits the activity of the digestive enzyme alpha amylase. This results in delaying or attenuating the absorption of starch and carbohydrates. At least 1 recent clinical trial has shown a modest, albeit statistically significant decrease in body mass index.

Willow Bark

Willow bark contains salicin, the ingredient that led to the introduction of aspirin. It has been used as an anti-inflammatory and antipyretic agent and was only recently hypothesized to be beneficial in weight loss.

Willow bark was ingested by a 25-year-old female with a history of an aspirin allergy in 1 case report.[45] Within 75 minutes of ingestion, the woman developed shortness of breath and itching and was admitted to the hospital and treated with diphenhydramine, epinephrine, methylprednisolone, and fluids. Patients with asthma or aspirin allergy should be cautioned against using products containing willow bark.

Yohimbine (Pausinystalia yohimbe)

Yohimbine is an alpha-2 receptor antagonist derived from an evergreen tree native to Central Africa.[30] In a randomized, double-blind, placebo controlled trial, 47 patients were assigned to yohimbine (peak dose, 43 mg/day) or placebo for 6 months.[46] Only 33 participants completed the trial. Outcomes included changes in body weight, BMI, total cholesterol, high-density lipoprotein, body fat, and fat distribution. At the end of the trial, there were no significant differences in any outcome measured.

In another randomized, double-blind study, 20 female patients consumed a 3-week low calorie diet and then received placebo or 5 mg yohimbine 4 times a day for 3 weeks.[47] Yohimbine significantly increased weight loss compared with placebo. However, adverse events documented in trials include hypertension, anxiety, and agitation.[30]