Dimenhydrinate is primarily used to treat nausea, vomiting, and dizziness caused by motion sickness. Dimenhydrinate has also been found to aid in the treatment of ear congestion.
Diphenhydramine is the primary constituent of dimenhydrinate and dictates the primary effect. The main difference relative to pure diphenhydramine is a lower potency due to being combined with 8-chlorotheophylline. By weight, dimenhydrinate is between 53% to 55.5% diphenhydramine.
8-Chlorotheophylline, a chlorinated derivative of theophylline, was added in order to counteract drowsiness. Theophylline is very closely related to caffeine and theobromine, mild central nervous systemstimulants. It was thought by scientists[who?] that by combining the antiemetic effects of diphenhydramine with a stimulant, the extreme drowsiness induced by the former could be mitigated somewhat by the latter. The sedation caused by diphenhydramine, however, is substantially stronger than the stimulation caused by 8-chlorotheophylline, so the overall effect is still mostly sedating.
Dimenhydrinate is used as a deliriant at doses of 1200 to 2000 mg, although body weight plays a significant part in dosing of this drug. Slang terms for Dramamine used this way include "dime," "dime tabs," "D-Q," "substance D," "d-house," and "drams." Abusing Dramamine is sometimes referred to as Dramatizing or "going a dime a dozen," a reference to the amount of Dramamine tabs generally necessary for a trip. The LD50 (the dose at which 50% of animals tested produced fatal symptoms) for dimenhydrinate is 500 mg/kg in lab rats, though there is no laboratory evidence of weight correlation so the same dose may likewise be fatal in 50 percent of humans.
Many users report a side effect profile consistent with tropane glycoalkaloidal (e.g. atropine) poisoning as both show antagonism of muscarinic acetylcholine receptors in both the central and autonomic nervous system, which inhibits various signal transduction pathways. In the CNS, dimenhydrinate readily crosses the blood-brain barrier, exerting effects within the visual and auditory cortex.
Other CNS effects occur within the limbic system and hippocampus, causing confusion and temporary amnesia due to decreased acetylcholine signaling. Toxicology also manifests in the autonomic nervous system, primarily at the neuromuscular junction, resulting in ataxia and extrapyramidal side-effects and the feeling of heaviness in the legs, and at sympathetic post-ganglionic junctions, causing urinary retention, pupil dilation, tachycardia, irregular urination, and dry red skin caused by decreased exocrine gland secretions, and mucous membranes. Considerable overdosage can lead to myocardial infarction (heart attack), serious ventricular dysrhythmias, coma and death. Such a side-effect profile is thought to give ethanolamine-class antihistamines a relatively low abuse liability. The specific antidote for dimenhydrinate poisoning is physostigmine, usually given by IV in a hospital.
Dimenhydrinate has successfully been used as an antiemetic and sedative in housepets. It is commonly used to reduce the effects of idiopathic vestibular syndrome. The suggested dosage is 50 mg for dogs and 10 mg for cats; duration of effect is 8 hours. This dosage is not a proper measure for all pets and should be adjusted by weight.
In United States, it is marketed under brand names Dramamine, Driminate, Gravol, Gravamin, Vomex, and Vertirosan. It is marketed in Brazil as Dramin, in Canada as Gravol, in Ecuador as Anautin, in Hungary as Daedalon, in Sweden as Amosyt, in Indonesia as Antimo, in Italy as Xamamina, in Peru as Gravicoll, in Poland as Aviomarin, in Portugal as Viabom, in Serbia as Dimigal, in Spain as Biodramina, and in Thailand as ไดเมนนีน (Daimenin). In Pakistan, it is marketed under brand name Gravinate.