Capsicum annuum (capsaicin)

What is Capsicum annuum (capsaicin)?

Capsicum annuum is the species that gives us bell peppers, jalapeños, paprika and cayenne. The heat comes from a family of compounds called capsaicinoids, of which capsaicin is the main one. Sweet peppers have almost none. Supplements use extracts standardised to a capsaicinoid content, often around 2 per cent, and some use coated beadlets, such as the branded Capsimax, designed to release in the gut rather than the mouth so the capsule does not burn on the way down. A related group, capsinoids, comes from a non-pungent pepper variety. Capsinoids act on the same receptor without the heat and have been studied separately.

How it works

Capsaicin activates a receptor called TRPV1, the same one that responds to heat. That is why chilli feels hot and why the body responds as if it were warming up: the sympathetic nervous system becomes slightly more active, the body burns a little more energy and shifts slightly towards burning fat. Some studies suggest it activates brown fat, a heat-producing tissue that adults have in small and variable amounts. Capsaicin may also reduce appetite through signals from the gut. All of this is well documented in short laboratory studies. The problem is scale. The extra energy burned is a few tens of calories a day, and the body adjusts to repeated exposure, which may be why the effect has not produced much weight loss over months.

What the research actually shows

Evidence strength varies by what is being claimed, so each use is graded separately against the published criteria rather than averaged into one reassuring letter.

Effective dosage

There is no single agreed oral dose. Trials of capsaicin for energy expenditure used widely varying amounts, from a few milligrams to more than 100 mg a day of capsaicin, often in food. The capsinoid trial used 6 mg a day. Branded capsicum extracts in supplements commonly provide 2 to 4 mg of capsaicinoids per serving, often from 100 to 200 mg of an extract standardised to about 2 per cent. Taking it with food reduces stomach irritation. If you want the appetite effect, it has only been shown when taken shortly before a meal.

Where products diverge from the research. Most fat burners that include capsicum list it inside a proprietary blend, so you cannot tell how much capsaicinoid you are getting. Where the amount is listed, it is often an extract weight rather than the capsaicinoid content. "Capsicum annuum 100 mg" at 2 per cent is 2 mg of capsaicinoids. Check whether the label gives the standardisation. The bigger gap, though, is between the mechanism and the promise. Even a product dosed exactly as in the trials delivers an effect measured in tens of calories.

Safety, side effects and interactions

Capsaicin is safe in food amounts for most people, but concentrated extracts can cause stomach pain, burning, heartburn, nausea and diarrhoea, particularly on an empty stomach. People with reflux, gastritis, ulcers or irritable bowel syndrome are likely to find it uncomfortable. Because it raises sympathetic activity, it is usually combined in fat burners with caffeine and other stimulants, and the combination is harder on the heart than capsicum alone. Anyone with high blood pressure or a heart rhythm problem should look at the whole formula, not just this ingredient. Capsaicin may interact with blood thinners and some blood pressure medicines, although the evidence is limited. Keep the capsules away from eyes and broken skin, and wash your hands after opening one.

None of this is medical advice. See the medical disclaimer for what that means before you act on anything here.