BENADRYL


Diphenhydramine is widely used in nonprescription sleep aids (Nytol, Sominex, Unisom, Compoz, Excedrin PM, etc.) with a 50mg recommended dose mandated by the FDA. In the United Kingdom, Australia, New Zealand, South Africa, and other countries, a 50 to 100mg recomended dose is permitted.

Recreational drug users sometimes take several times the recommended dose of diphenhydramine in order to attain an intense hallucinogenic (more accurately, delirious) state. The mental effects are described by many as "dreaming while awake" involving visual and auditory hallucinations which, unlike those experienced with most psychedelics, often cannot be readily distinguished from reality. Many users report a side effect profile consistent with tropane glycoalkaloidal poisoning. This is due to antagonism of muscarinic acetylcholine receptors in both the central and autonomic nervous system, inhibiting various signal transduction pathways. In the CNS, diphenhydramine readily crosses the blood-brain barrier, exerting effects within the visual and auditory cortex, accounting for reported visual and auditory disturbances. Other CNS effects occur within the limbic system and hippocampus, causing confusion and temporary amnesia. Toxicology also manifests in the autonomic nervous system, primarily at the neuromuscular junction, resulting in ataxia and extrapyramidal side-effects, and at sympathetic post-ganglionic junctions, causing urinary retention, pupil dialation, tachycardia, and dry skin & mucous membranes. Considerable overdosage can lead to myocardial infarction, serious ventricular dysrhythmias, coma and death. Such a side-effect profile is thought to give ethanolamine-class antihistamines a relatively low abuse liability.