Antihistamine
The vast majority of marketed H-antihistamines are receptor antagonists and only a minority of marketed compounds are inverse agonists at the receptor. Clinically, H-antihistamines are used to treat allergic reactions and mast cell-related disorders. Sedation is a common side effect of H-antihistamines that readily cross the blood–brain barrier; some of these drugs, such as diphenhydramine and doxylamine, are therefore used to treat insomnia. H-antihistamines can also reduce inflammation, since the expression of NF-κB, the transcription factor the regulates inflammatory processes, is promoted by both the receptor's constitutive activity and agonist (i.e., histamine) binding at the H receptor.
Iprindole
Anticholinergic side effects such as dry mouth and constipation are either greatly reduced in comparison to imipramine and most other TCAs or fully lacking with iprindole. However, it still has significant antihistamine effects and therefore can produce sedation, though this is diminished relative to other TCAs similarly. Iprindole also lacks significant alpha-blocking properties, and hence does not pose a risk of orthostatic hypotension.