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.
Temazepam
Chronic or excessive use of temazepam may cause drug tolerance, which can develop rapidly, so this drug is not recommended for long-term use. In 1979, the Institute of Medicine (USA) and the National Institute on Drug Abuse stated that most hypnotics lose their sleep-inducing properties after about three to 14 days. In use longer than one to two weeks, tolerance will rapidly develop towards the ability of temazepam to maintain sleep, resulting in a loss of effectiveness. Some studies have observed tolerance to temazepam after as little as one week's use. Another study examined the short-term effects of the accumulation of temazepam over seven days in elderly inpatients, and found little tolerance developed during the accumulation of the drug. Other studies examined the use of temazepam over six days and saw no evidence of tolerance. A study in 11 young male subjects showed significant tolerance occurs to temazepam's thermoregulatory effects and sleep inducing properties after one week of use of 30-mg temazepam. Body temperature is well correlated with the sleep-inducing or insomnia-promoting properties of drugs.