H1 antihistamines interact with central sigma receptors.

Several antihistamines were evaluated for their ability to interact with sigma, muscarinic and histaminic H1 binding sites in rat brain preparations. All of the antihistamines were able to interact with the sigma site, as well as the other two sites. In addition, tripelennamine was found to elicit sigma-like behaviors when administered to rats. This affinity for the sigma site suggests that the compounds may elicit some of their undesirable CNS side effects via this interaction.