Dimenhydrinate (marketed under brand names Dramamine, Gravol and Vertirosan) is an over-the-counter drug used to prevent nausea and motion sickness.

It is most commonly used as pills, although it is also available in liquid form and in suppositories. This last is particularly useful in the case of persistent vomiting.

It is closely related to diphenhydramine HCl, or Benadryl. The differences relate to the weight-for-weight potency (50 mg dimenhydrinate contains 29 mg of the drug diphenhydramine), delay of action (dimenhydrinate must dissociate into diphenhydramine and its counterion in the body before it is active, therefore diphenhydramine produces effects sooner), and degree of sedation produced. Chemically, dimenhydrinate is a salt of two drugs: diphenhydramine and 8-chlorotheophylline, a chlorinated derivative of the theophylline. Theophylline is very closely related to caffeine and theobromine, mild central nervous system stimulants. It was thought 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. In actuality, the sedation caused by diphenhydramine is substantially stronger than the stimulation caused by chlorotheophyllinate. Diphenhydramine, an ethanolamine-class antihistamine, is found in most OTC sleep aids and allergy preparations, such as Tylenol PM and Benadryl. It is primarily a H₁-antagonist, but also possesses an antimuscarinic effect. It is used in Dramamine to prevent nausea and emesis; however, the development of the chemical meclizine has overtaken its usage (marketed as "Dramamine II") because meclizine doesn't produce as much drowsiness.

Recreational use

The mental effects can be described as "dreaming while awake" involving visual and auditory hallucinations that, unlike those experienced with most psychedelic drugs, often cannot be readily distinguished from reality. People who consume a high recreational dose can possibly find themselves interacting normally with a hallucination and have normal conversations with, for example, a hallucination of a family member. A common sometimes frightening hallucination is of insects and spiders. Hallucinations are more frequent and unpleasant in a setting with little or no light. Inexperienced users of deliriants are likely to panic.

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 acetycholine. 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 hospital.

The intoxication can be described with the following saying “blind as a bat, dry as a bone, red as a beet, mad as a hatter, and hot as a hare." Blind as a bat meaning blurry and impaired vision. Dry as a bone meaning the inhibiting effect on sweat and saliva making the mouth and skin dry as a "bone." Red as beet meaning the observed effect of the skin turning red with someone using deliriants. Mad as hatter referring to the frank delirium and true hallucinations (unlike LSD or Psychedelic Mushrooms; which only cause alterations in perception, deliriants cause true hallucinations as they can't be distinguished from reality and are usually extremely real looking) induced effect. Hot as a hare meaning the user of the deliriant becomes extremely hot because of lack of sweat and saliva production and significant increase in heart rate and blood pressure.

Veterinary use

References

Dramamine is covered by Sun Kil Moon, appearing on their Tiny Cities album.