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.
Butriptyline
Butriptyline has potent antihistamine effects, resulting in sedation and somnolence. It also has potent anticholinergic effects, resulting in side effects like dry mouth, constipation, urinary retention, blurred vision, and cognitive/memory impairment. The drug has relatively weak effects as an alpha-1 blocker and has no effects as a norepinephrine reuptake inhibitor, so is associated with little to no antiadrenergic and adrenergic side effects.