Capsaicin is a type of capsaicinoid, a category of alkaloids often found in fruits of the Capsicum genus of the Solanaceae family. Capsaicin is known for its role in making chili peppers spicy.

Capsaicin and its analogues (e.g., capsiate, a non-spicy capsaicinoid) show promise as preworkout ergogenic supplements, producing small improvements in performance on strength-based exercises (e.g., squats) when taken about 45 minutes before a workout.^[2][3]

Capsaicinoids like capsaicin might lead to weight loss, but the effect seems very small, if it exists at all.^[4] Intriguingly, two clinical trials found that capsaicinoids led to a decrease in abdominal/visceral fat (with no change in total body fat levels).^[5][6]

Consuming foods high in capsaicin (e.g, chili peppers) is associated with a lower risk of early death, possibly mediated by a reduction in heart disease mortality.^[7]

Topical application of capsaicin can be helpful for nerve pain, with analgesic effects reported in the context of diabetes and HIV-associated neuropathy as well as shingles-related neuralgia.^[8][9] Topical capsaicin may also reduce pain due to osteoarthritis.^[10][11]

Ingestion of capsaicin-containing foods causes a burning sensation to the mouth that can be unpleasant (although some people find it enjoyable, possibly due to endorphin release^[12]). Topical capsaicin can result in a burning sensation at the application site.

Capsaicin can provoke adverse gastrointestinal (GI) symptoms (e.g., abdominal pain, diarrhea, and heartburn), especially in high dosages and in people with GI disorders (e.g., irritable bowel syndrome, gastroesophageal reflux disease (GERD)).^{[13][14][15][16]} There is some evidence that GI symptoms subside with regular consumption, although more research is needed.^[17][18]

Case-control studies have frequently observed an association between chili pepper consumption and a higher risk of stomach cancer.^[19] However, this finding remains controversial, given the limitations of case-control evidence and the fact that the China Kadoorie Biobank study, one of the highest quality studies on the topic, found that people who ate chili peppers more frequently actually seemed to have a lower risk of stomach cancer.^[20]

Most of capsaicin’s effects are mediated by a protein called transient receptor potential vanilloid subtype 1 (TRPV1). TRPV1 is found throughout the body, including the oral cavity, nervous system, skeletal muscles, and adrenal glands.^[21][22][23] By activating TRPV1, capsaicin can create the sensation of heat (e.g., in the mouth), promote sweat release, stimulate adrenaline release, increase metabolic activity in skeletal muscles, and inhibit sensory neurons responsible for transmitting feelings of pain.^[22][24][25]