This results, by an unknown mechanism, in transient phase advances. Antihistamines and Sleep Architecture Antihistamines certainly affect sleep, the commonest example being the drowsiness induced by some hay fever remedies. The histamine theory may help explain why some antihistamines alter sleep architecture. However, antihistamines are normally taken during the day, when H2 receptors seem to entrain the circadian patterns. So, whether they will hang around long enough to block the nocturnal H1 receptor mediated entrainment mechanism, and thus alter the user s sleep architecture, depends on their half-life.
Research is hampered by the lack of an appropriate animal model.
Timmerman remarks that most studies used nocturnal animals, such as rats. Nevertheless, the research may eventually open a market for drugs that help us live with altered circadian rhythms. He proposes using receptor-knockout mice, antisense techniques, and pharmacological manipulation of circadian rhythms by selective receptor agonists and antagonists to examine the neurochemical modulate of suprachiasmatic nucleus. And he is optimistic about the prospects. However, three subtypes of histamine receptors are present throughout the brain and side-effects may be possible.