Amines are organic derivatives of ammonia. They are formed by replacing one or more ammonia protons with alkyl or aryl groups. Depending upon the number of organyl groups bonded to nitrogen, amines are classified as primary, secondary, or tertiary. Primary amines have one organyl group attached to the nitrogen atom, while secondary and tertiary amines have two and three organyl groups attached to the nitrogen atom, respectively.

When a fourth organyl group is present, the nitrogen possesses a formal positive charge. Such amines exist as quaternary ammonium salts.

Amines are also classified as aliphatic and aromatic amines. An amine is aliphatic when only alkyl groups are bonded to the nitrogen atom. In an aromatic amine, at least one aryl group is bonded to the nitrogen atom. If the nitrogen atom is part of a ring, such amines are classified as heterocyclic amines. Further, if nitrogen is heteroatom in an aliphatic ring, such amines are classified as heterocyclic aliphatic amines. In the same way, an amine is classified as heterocyclic aromatic amine if the nitrogen is part of the aromatic ring.

Nitrogen-containing molecules of plant origin are known as alkaloids. Most of them are physiologically active in the human body. For example, ingestion of coniine, a heterocyclic aliphatic amine, can lead to respiratory issues, weakness, or death in severe cases. Cocaine, a tertiary amine, obtained from the coca plant leaves, stimulates the central nervous system when consumed.