The main ingredient in fat burners or thermogenics is ephedrine, a synthetic version of a chinese herb ephedra, or also known as ma huang.

Ephedrine is a drug, rather than a nutrition supplement. It is also used in low concentrations in flu and cold remedies (pseudoephedrine).

Ephedrine is chemically similar to amphetamines, which act on the brain and the central nervous system.

There is some evidence that ephedrine helps fat loss: partly due to an increase in thermogenesis, partly because it suppresses your appetite and partly because it makes you more active.

When taken as an ECA stack (ephedrine – caffeine – aspirin) ephedrine has a greater effect in terms of weight loss and thermogenesis. However the fat burning effect of ephedrine seems to decrease over time.

Ephedrine is judged to be safe in doses between 18-25 mg, that’s the amount that’s used in cold remedies. Doses more than 32 mg a day may triple your risk of bleeding in the brain. Prolonged use and higher doses combined with heavy exercise increase your risk of side effects, like increased heart rate, increased blood pressure, palpitations, anxiety, nervousness, insomnia, headaches, nausea, vomiting and dizziness.

Ephedrine is addictive, and people can develop a tolerance to it, which means you will need to take more and more to get the same effects.