Weight-loss supplements that actually work, according to research

By Alistair Gardiner
Published June 16, 2021

Key Takeaways

In the US, more than two-thirds of adults and roughly one-third of children are overweight or obese, and, according to the National Institutes of Health Office of Dietary Supplements (NIHODS) 45% of overweight Americans and 65% of obese Americans are trying to lose weight. 

Weight management advice is pretty straightforward. Develop healthy eating habits, eat fewer calories, and stay active. But what sounds simple actually amounts to a monumental effort. 

Most will need help on this journey, and for some, supplements may be the answer. 

Weight-loss supplements are popular, with roughly 15% of US adults trying them at some point. Americans spend roughly $2.1 billion annually on weight-loss dietary supplements in pill form. These products make a variety of claims, including the ability to reduce macronutrient absorption, suppress appetite, increase metabolism, and promote thermogenesis.

While some of these claims may be tenuous, others have scientific support. Here are five weight-loss supplements that studies indicate can make a difference.


Many dietary and weight-loss supplements contain caffeine--including some that don’t list it as an ingredient, or don’t declare the amount that the product contains. According to the NIHODS, caffeine is a methylxanthine, which stimulates the central nervous system, heart, and skeletal muscles; prompts gastric and colonic activity; acts as a diuretic; and increases thermogenesis. It also increases fat oxidation through sympathetic activation of the central nervous system and can lead to increased fluid loss. Caffeine may aid weight loss through all these means. 

That said, the NIHODS emphasizes that most studies evaluating caffeine’s impact on weight management have had short durations and focused on a combination of products. As a result, evidence for its efficacy remains murky. While some studies have found that groups who supplement their diet with caffeine-rich products have lost more than twice as much weight as control groups, others found differences that were less statistically significant. Findings are heterogeneous, but most studies indicate that caffeine appears to facilitate weight loss, to some extent. 

Up to 400 mg of caffeine daily is considered safe, although it may cause sleep disturbances and jitteriness in some. 

Green Tea Extract

Like caffeine, green tea extract contains catechins, which are flavonoids with antioxidant properties. One cup of green tea has roughly 240–320mg of catechins and 45 mg caffeine. According to the NIHODS, evidence suggests that consuming green tea may reduce body weight by “increasing energy expenditure and fat oxidation, reducing lipogenesis, and decreasing fat absorption.”

The NIHODS cites several reviews of studies, which linked green tea catechin consumption with weight loss. Most of these studies involved the intake of both catechins and caffeine, which suggests that the two ingredients may act synergistically. 

According to NIHODS, there are no risks of adverse health effects from consuming green tea as a beverage, and most reported adverse effects from green tea extract are mild to moderate (including nausea and abdominal discomfort).

Bitter Orange

Bitter orange is the common name of Citrus aurantium, a fruit that contains p-synephrine and other protoalkaloids. The synephrine alkaloids purportedly mimic the effects of epinephrine and norepinephrine, leading to increased energy expenditure, lipolysis, and a suppressed appetite.  

Supplements typically combine bitter orange with other ingredients, limiting our understanding of its efficacy. Still, most evidence suggests that bitter orange can aid in weight loss. In one study, for example, a group of 20 overweight adults consumed supplements containing 975 mg bitter orange extract, 528 mg caffeine, and 900 mg St. John’s wort, or a placebo. Those taking the treatment had a significantly greater reduction in body fat than the control group. 

However, according to NIHODS, some products containing bitter orange may raise safety concerns, with reported adverse effects including chest pain, headache, anxiety, elevated heart rate, and others. Since supplements often contain multiple ingredients, it’s unclear whether bitter orange or other substances were responsible for these negative health outcomes. 

Conjugated Linoleic Acid

Conjugated linoleic acid (CLA) is present in dairy products and beef, but is also available in dietary supplements as a triacylglycerol or as a free fatty acid. Research suggests that CLA assists with weight loss by reducing lipogenesis, increasing lipolysis and fatty acid oxidation in skeletal muscle, and promoting apoptosis in adipose tissue.

While there is a fair amount of evidence for CLA’s weight management qualities, much of the corresponding research has been conducted on animals. Some studies, however, indicate its efficacy in humans, too. For example, one study examined the effects of CLA supplementation on 180 overweight male and female volunteers, over a year. Researchers found that those who received CLA had lost far more body fat mass than those taking a placebo.

According to the NIHODS, CLA is well-tolerated and most reported adverse effects (primarily gastrointestinal disturbances) are minor. 


Capsaicin, the substance that gives chili peppers their fiery heat, has long been thought to have anti-obesity effects, due to its ability to increase energy energy expenditure and lipid oxidation, mediate insulin responses, and increase feelings of fullness. 

While studies have indicated that capsaicin can aid weight-loss, they have primarily focused on energy intake and appetite, rather than body weight. However, evidence from those studies is compelling. For example, a review published in Bioscience Reports in 2017 cites several studies that found that capsaicin supplementation can result in abdominal fat loss, increased resting energy expenditure, and enhanced lipid oxidation. 

According to NIHODS, supplementing 4 mg of capsaicin daily may cause gastrointestinal distress, but is otherwise safe. 

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