Fexofenadine is a second-generation, long lasting H1-receptor antagonist (antihistamine) which has a selective and peripheral H1-antagonist action. Histamine is a chemical that causes many of the signs that are part of allergic reactions, such as the swelling of tissues. Histamine is released from histamine-storing cells (mast cells) and attaches to other cells that have receptors for histamine. The attachment of the histamine to the receptors causes the cell to be "activated," releasing other chemicals which produce the effects that we associate with allergy. Fexofenadine blocks one type of receptor for histamine (the H1 receptor) and thus prevents activation of cells by histamine. Unlike most other antihistamines, Fexofenadine does not enter the brain from the blood and, therefore, does not cause drowsiness. Fexofenadine lacks the cardiotoxic potential of terfenadine, since it does not block the potassium channel involved in repolarization of cardiac cells. Fexofenadine is sold under the trade name Allegra among others. ALLEGRA is indicated for the relief of symptoms associated with seasonal allergic rhinitis in adults and children 2 years of age and older.

Terfenadine under brand name Seldane was used for the treatment of allergic rhinitis and allergic skin disorders but was withdrawn because of the serious side effect, heart rhythm problems. Terfenadine is a potent antagonist of histamine H1-receptor-mediated responses.

Azacyclonol (aka gamma-pipradrol) is an ataractive agent; a compound which diminished hallucinations in psychotic individuals. It is sometimes referred to as a tranquilizer or antipsychotic, though it does not actually possess these properties. It was used in Europe during the 1950's for treatment of schizophrenia; likely to reduce the psychedelic effects of LSD and mescaline. However, it had mixed clinical effectiveness and did not gain widespread adoption and was eventually discontinued. Azacyclonol was sold under several trade names: Ataractan, Calmeran, Frenoton, Frenquel and Psychosan.