Overview

Diphenhydramine, available as the brand name Benadryl and dimenhydrinate, available as Dramamine, are very closely related medications. Interestingly enough, dimenhydrinate actually contains diphenhydramine, which is discuss below.

Benadryl (Diphenhydramine)

Benadryl Diphenhydramine Structure

Benadryl contains diphenhydramine, a sedating first generation antihistamine.

In addition to its use for allergies, it is beneficial in the treatment with vertigo related to motion sickness and insomnia, due to its sedating properties.

Due to the sedating properties of diphenhydramine, it is a common ingredient in over the counter sleep products, such as ZzzQuil.

Benadryl (diphenhydramine) is given in doses of 25-50mg every four to six hours.

Section Summary
Benadryl contains 'diphenhydramine', a sedating 'first-generation' antihistamine. 

Dramamine (Dimenhydrinate)

Dimenhydrinate Structure

Dimenhydrinate consists of two chemical compounds, bound together:

  • Diphenhydramine
  • 8-chlorotheophylline

Specifically, dimenhydrinate is classified as a "chlorotheophylline salt of diphenhydramine". In fact, dimenhydrinate contains nearly 55% diphenhydramine by weight! 

8-chlorotheophylline is a chemical derivative of theophylline, which itself is structurally similar to caffeine.

As such, 8-chlorotheophylline has mild stimulating effects.

However, the stimulant effect of 8-chlorotheophylline is quite small and dimenhydrinate has an overall sedative effect in most individuals.

The commonly used doses of dimenhydrinate reflect the fact that it contains nearly 50% diphenhydramine. While Benadryl (diphenhydramine) is typically given at 25-50mg per dose, Dramamine (dimenhydrinate) is typically given at 50-100mg per dose.

Dimenhydrinate is more commonly used for symptoms of nausea and motion sickness than Benadryl since it may cause slightly less sedation.

In addition, it may be slightly more effective for the following off-label nausea related symptoms, due to the addition of 8-chlorotheophylline:

  • Meniere's syndrome
  • Hyperemesis gravidarum (severe nausea and vomiting during pregnancy)

 

Section Summary
Dramamine consists of diphenhydramine bound to 8-chlorotheophylline. 8-chlorotheophylline has mild stimulant effects and can slightly off-set the sedation of diphenhydramine.

Summary

  • Diphenhydramine (Benadryl) is a first generation antihistamine used for the treatment of allergies and insomnia, due to its sedative effect.
  • Dimenhydrinate (Dramamine) is a drug compound that contains around 55% diphenhydramine and 45% 8-chlorotheophylline.
  • Dimenhydrinate may cause slightly less sedation than diphenhydramine and is commonly used off-label for Meniere's syndrome and hyperemesis gravidarum.