25 to 50 milligrams of diphenhydramine, brand name Benadryl, may be taken 30 minutes before bedtime by adults and children over the age of 12 for the treatment of insomnia, according to Drugs.com. The medication should not be used to induce sleep in children younger than 12.
Drowsiness, dizziness and weakness, dry nose, eyes and mouth, constipation and nausea are among the more common side effects of the medication, notes Everyday Health. Headaches, appetite loss and chest tightness may also occur. In children, restlessness and excitability is common. Serious side effects include vision changes, difficulty with urination and trouble breathing. If they develop, the medication should be stopped and a physician contacted at once.
Other medications causing drowsiness will interact with diphenhydramine, says WebMD. Examples of these medications include muscle relaxants, narcotic pain relievers, benzodiazepines for anxiety and panic disorders and other antihistamines. Alcohol will also add to the effects of diphenhydramine. To avoid overdose, the oral form of the medication should not be combined with topical forms, such as creams or lotions used to treat rashes. Combination cough and cold products often contain diphenhydramine and should not be combined with additional oral doses of the medication.
Diphenhydramine is an antihistamine used to treat the nasal and eye symptoms associated with allergies and upper respiratory infections, explains WebMD. It is also used to treat rashes and itching associated with allergic reactions to medications or other substances, to prevent nausea and vomiting due to motion sickness, and to induce relaxation and sleep.