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.
Allylestrenol
Side effects of allylestrenol are few and have not been well-defined, but are assumed to be similar to those of related medications (i.e., other progestins). When used at high dosages in the treatment of BPH in men, allylestrenol can cause symptoms of hypogonadism and sexual dysfunction. The medication indeloxazine may be able to counteract allylestrenol-associated sexual dysfunction. Allylestrenol has no androgenic or other off-target hormonal side effects.