Trimethylamine (TMA) is an organic compound with the formula N(CH3)3. This colorless, hygroscopic, and flammable tertiary amine has a strong "fishy" odor in low concentrations and an ammonia-like odor at higher concentrations. It is a gas at room temperature but is usually sold in pressurized gas cylinders or as a 40% solution in water. TMA is a nitrogenous base and can be readily protonated to give trimethylammonium cation. Trimethylammonium chloride is a hygroscopic colorless solid prepared from hydrochloric acid. Trimethylamine is a good nucleophile, and this reaction is the basis of most of its applications.
Trimethylamine is a product of decomposition of plants and animals. In humans, it is synthesized exclusively by gut microbiota from dietary nutrients such as choline and carnitine. High levels of trimethylamine are associated with the development of fish odor syndrome and atherosclerosis, which arise from the foul, fishy odor of trimethylamine and the proatherogenic property of its metabolite, trimethylamine N-oxide, respectively. TMA is the substance mainly responsible for the odor often associated with rotting fish, some infections, bad breath and can be a cause of vaginal odor due to bacterial vaginosis. It is also associated with taking large doses of choline and carnitine.
In 2013, trimethylamine was identified as a potent full agonist of human TAAR5, a trace amine-associated receptor that is expressed in the olfactory epithelium and functions as an olfactory receptor for tertiary amines. One or more additional odorant receptors appear to be involved in trimethylamine olfaction in humans as well.