Many people tolerate thermogenic supplements just fine, but they can cause unpleasant side effects in some ( 34 , 35 ). The most common complaints include nausea, constipation, abdominal pain and headache. What's more, these supplements may lead to a slight increase in blood pressure ( 8 , 29 , 30 , 36 ).
This article reviews the most popular thermogenic supplements, their effectiveness, safety and side effects.
While these ingredients certainly have small, positive effects on metabolism, it’s unclear whether these effects are significant enough to help people lose weight or body fat.
Some of the most popular thermogenic supplements include caffeine, green tea, capsaicin and other plant extracts.
Thermogenic supplements contain natural ingredients designed to boost your metabolism and increase fat burning.
Thermogenic supplements boost metabolism, increase fat burning and reduce appetite. They’re available without a prescription and can contain just one ingredient or a blend of thermogenic compounds.
Manufacturers claim that these supplements will help you lose weight or burn more body fat, but the veracity of this claim is hotly debated.
Some contain just one ingredient, while others use a blend of metabolism-boosting compounds.
Many different types of these supplements are available over the counter.
When your body burns calories, it generates more heat, so supplements that boost metabolism or fat burning are considered thermogenic.
Here’s some of the research behind the most popular thermogenic compounds to determine if they actually help burn body fat.
1. Caffeine
Caffeine is a stimulant naturally found in over 60 different plants, including coffee, cocoa, tea, kola nut, guarana and yerba mate ( 1 , 2 ).
It increases levels of adrenaline, a hormone that stimulates your fat cells to release fatty acids into your bloodstream, where they can be used by your cells for energy.
This stimulant also reduces appetite and boosts metabolism, helping you burn more calories while eating less ( 3 ).
Research has found that every milligram of caffeine consumed helps burn an additional 0.1 calories in the following 24 hours. This means that taking a 150-mg caffeine pill would burn an additional 15 calories over the course of a day ( 4 ).
Human and animal studies show that doses of 1.4–2.3 mg of caffeine per pound (3–5 mg per kg) of body weight are most effective in boosting metabolism and increasing fat burning ( 3 ).
Since caffeine’s effects on metabolism are relatively small, supplementing is unlikely to make a huge impact on body weight but may help when combined with other diet and exercise changes.
2. Green Tea / EGCG
Green tea contains two compounds that have thermogenic effects: caffeine and epigallocatechin gallate (EGCG) ( 5 , 6 ).
As noted above, caffeine stimulates the release of adrenaline, which boosts metabolism and increases fat burning. EGCG enhances these effects by slowing the breakdown of adrenaline so that its impact is amplified ( 6 , 7 ).
Research has found that caffeinated green tea supplements can increase metabolism by roughly 4% and boost fat burning by 16% for 24 hours after ingestion ( 4 ).
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However, it’s unclear whether this effect leads to significant weight loss or reductions in body fat.
One review found that overweight or obese people who consumed green tea supplements daily for at least 12 weeks lost only 0.1 pounds (0.04 kg) and reduced their waist size by just 0.1 inches (2 cm) ( 8 ).
However, a different review found that individuals who took green tea supplements for the same time period experienced an average weight loss of 2.9 pounds (1.3 kg), regardless of the dose taken ( 9 ).
More research is needed to better understand how green tea affects metabolism and body composition.
3. Capsaicin
Capsaicin is the molecule that makes chili peppers spicy — the spicier the pepper, the more capsaicin it contains.
It also reduces appetite, making you eat fewer calories. Together, these effects make capsaicin a powerful thermogenic substance ( 11 ).
A review of 20 studies found that capsaicin supplements can boost metabolism by about 50 calories per day, which could lead to significant weight loss over time ( 12 ).
Another study showed that dieters taking 2.5 mg of capsaicin with each meal burned 10% more fat in the subsequent 24 hours, compared to a control group ( 13 ).
Supplementing with 6 mg of capsaicin daily has also been linked to reductions in belly fat over a three-month period ( 14 )
However, there is some evidence that your body can adapt to capsaicin, reducing these effects over time ( 15 ).
4. Garcinia Cambogia
Garcinia cambogia is a tropical fruit whose extracts are often used in weight loss supplements.
It contains a compound called hydroxycitric acid (HCA) that can block the activity of the enzyme ATP citrate lyase, which is involved in the formation of body fat ( 16 ).
A review of 12 studies found that taking garcinia cambogia supplements over 2–12 weeks leads to a 1% greater reduction in body weight compared to a placebo, on average. This is a difference of roughly 2 pounds (0.9 kg) ( 17 ).
However, there is no consensus on garcinia cambogia’s fat impact, since other research results have been mixed ( 18 , 19 , 20 , 21 ).
More studies are needed to understand whether garcinia cambogia supplements are effective for weight loss or reducing body fat.
5. Yohimbine
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Yohimbine is a chemical derived from the bark of the African yohimbe tree, and is commonly taken as a thermogenic supplement.
It works by increasing the activity of several hormones, including adrenaline, noradrenaline and dopamine, which could theoretically boost fat metabolism ( 22 , 23 ).
The effectiveness of yohimbine for fat loss has not been researched much, but early results are promising.
One small study found that professional athletes who took 20 mg of yohimbine daily for three weeks had 2% less body fat than athletes taking a placebo ( 24 ).
Yohimbine may be especially effective for weight loss when combined with exercise, since it has been shown to boost fat burning during and after aerobic exercise ( 25 ).
At present, there is not enough research to determine whether yohimbine truly helps burn body fat.
6. Bitter Orange / Synephrine
Bitter orange, a type of citrus fruit, contains synephrine, a compound that is a natural stimulant, similar in structure to ephedrine.
While ephedrine has been banned in the United States due to reports of sudden heart-related deaths, synephrine has not been found to have the same effects and is considered safe to use in supplements ( 26 ).
Taking 50 mg of synephrine has been shown to increase metabolism and burn an additional 65 calories per day, which could potentially help people lose weight over time ( 27 ).
A review of 20 studies using bitter orange alone or in combination with other herbs found that it significantly increased metabolism and weight loss when taken daily for 6–12 weeks ( 28 ).
No studies have attempted to determine whether it reduces body fat in humans.
7. Thermogenic Blends
Since many substances have thermogenic effects, companies often combine several of them in one supplement, hoping for greater weight loss effects.
Studies show that these blended supplements provide an extra metabolism boost, especially when combined with exercise. However, there have not been many studies to determine whether they reduce body fat ( 29 , 30 , 31 , 32 ).
One eight-week study found that overweight and obese dieters who took a daily supplement containing green tea extract, capsaicin and caffeine lost an additional pound (0.454 kg) of body fat, compared to a placebo. Yet, more research is needed ( 33 ).
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