Benefits
Body weight and waist size in overweight adults
Pooling 15 randomized trials in 762 overweight or obese adults, capsaicin lowered body weight by 0.51 kg, BMI by 0.25 kg/m2 and waist circumference by 1.12 cm more than control, with no change in waist-to-hip ratio. The authors described these effects as rather modest: about half a kilogram over the length of a trial.
Small rise in energy expenditure, none measurable in leaner people
Pooling 9 human studies, capsaicin or its non-pungent relative capsiate raised energy expenditure by about 59 kcal a day and lowered the respiratory quotient, a gas-exchange sign that more fat was burned. The effect appeared only in studies whose participants averaged a BMI above 25; in leaner groups neither measure changed.
Appetite: about 74 kcal less eaten at the next meal
Pooling 8 trials in 191 people, capsaicinoids taken before a meal reduced what people then ate by about 74 kcal at that meal, and at least 2 mg was needed. Trials differed widely (I2 = 75.7 percent), so the size of the effect is uncertain, and only a single meal was measured, not daily intake or body weight. The pooled analysis did not assess GLP-1 hormone levels.
Muscular endurance in short exercise tests; no aerobic endurance gain
Across 14 small studies (183 people), usually 12 mg taken 45 minutes before exercise, capsaicin or capsiate did not improve aerobic endurance such as time trials. It gave a small gain in repetitions to failure (effect size 0.27) and slightly lower perceived effort after those tests. These were single-session studies.
Cholesterol, blood pressure and blood sugar: no reliable change
Pooling 13 randomized trials in 821 adults, red pepper or capsaicin did not change triglycerides, LDL, HDL, systolic blood pressure, fasting glucose, insulin, HOMA-IR or HbA1c. Small drops in total cholesterol and diastolic blood pressure disappeared when one study was removed, and the certainty of the evidence was rated low to very low.
Topical capsaicin for pain is a separate product
Capsaicin creams and the 8 percent skin patch are used for nerve and joint pain, where reviews found that a minority of users get meaningful relief and that burning at the application site is common. That effect comes from applying capsaicin to the skin; swallowing a capsule does not deliver it.
Stomach lining in one 18-person chili study
In a crossover study, 18 healthy volunteers who ate 20 g of chili half an hour before a 600 mg aspirin dose had less stomach lining injury on endoscopy 6 hours later than when they took the aspirin with water. That was chili eaten as food in a one-day experiment, not a capsule taken daily, and capsaicin supplements can cause stomach burning in some people.
Mechanism of action
TRPV1 receptor activation
Capsaicin and capsiate both bind TRPV1, the receptor that senses heat. Capsaicin activates it on the tongue, which causes the burn, while capsiate is broken down as it crosses the lining of the mouth, which is why it is not hot.
Energy expenditure and fat use
TRPV1 activation is linked to a rise in energy expenditure and fat oxidation. In a mouse study, capsaicin improved swimming endurance, an effect attributed mainly to greater use of fat for fuel; whether this explains the small human effects has not been shown.
Muscle and perceived effort (proposed)
TRPV1 is also present in skeletal muscle, where its activation may increase calcium release inside muscle fibers and raise force output. Lower perceived exertion and nitric oxide release are other proposed routes. These are proposed explanations; the exercise studies did not measure them.
Food choice at the next meal
In the pooled appetite studies, the drop in energy intake appeared to come from a shift in preference toward carbohydrate-rich foods and away from higher-fat foods.
Skin desensitization (topical use only)
On the skin, capsaicin first increases sensitivity, then reduces it, and repeated or high-concentration application leaves pain-sensing nerve endings desensitized. This explains the topical pain effect and does not apply to oral capsules.
Clinical trials
Systematic review and meta-analysis of 15 randomized controlled trials of capsaicin supplementation published to May 2022 (Zhang et al. 2023, Br J Nutr)
762 overweight or obese adults across the pooled trials.
Compared with control, capsaicin reduced BMI by 0.25 kg/m2, body weight by 0.51 kg and waist circumference by 1.12 cm, with no effect on waist-to-hip ratio. The authors judged the effects rather modest.
Meta-analysis of 9 human studies of capsaicin or capsinoid intake, out of 627 screened (Zsiborás et al. 2018, Crit Rev Food Sci Nutr)
Adults in the pooled studies, analysed by whether their average BMI was above or below 25.
Energy expenditure rose by 58.56 kcal a day and the respiratory quotient fell by 0.216, suggesting more fat oxidation. Studies whose participants averaged a BMI below 25 showed no effect on either measure; the effect was confined to studies averaging a BMI above 25.
Systematic review and meta-analysis of 8 trials with energy intake data, 19 effect sizes (Whiting et al. 2014, Appetite)
191 participants across the pooled trials.
Capsaicinoids taken before a meal reduced ad libitum energy intake at that meal by 74 kcal. Heterogeneity was high (I2 = 75.7 percent), and at least 2 mg of capsaicinoids appeared necessary. Only single-meal intake was measured.
Meta-analysis of 14 placebo-controlled studies, most using 12 mg 45 minutes before exercise (Grgic et al. 2022, Nutrients)
183 participants performing aerobic tests (time trials, time to exhaustion) or resistance sets to failure.
No effect on aerobic endurance (effect size 0.04, p = 0.69). A small improvement in muscular endurance (effect size 0.27, p = 0.002) and lower perceived exertion after muscular endurance tests but not after aerobic tests.
Cochrane systematic review of 8 randomized, double-blind studies of a single 8 percent capsaicin skin patch, mostly against a 0.04 percent patch as active placebo (Derry et al. 2017, Cochrane Database Syst Rev)
2,488 adults with nerve pain after shingles, HIV-related nerve pain, painful diabetic nerve damage or pain after hernia repair.
About 10 percent more people were much or very much improved with the high-concentration patch than with the low-concentration control at 8 and 12 weeks. Evidence quality was moderate to very low, local skin reactions were common, and serious adverse events were similar between groups. This is a drug patch applied to the skin, not a supplement.