Diphenhydramine is also used to prevent and treat motion sickness ...

Diphenhydramine should not be given to children younger than 2 years old because it may cause serious or life-threatening side effects in young children. Diphenhydramine should not be given to children older than 2 years old but younger than 6 years old unless prescribed by a doctor and should be used carefully in children who are 6-11 years old. Diphenhydramine should not be used to cause sleepiness in children younger than 12 years of age.

... When diphenhydramine is used to treat motion sickness, it is usually taken 30 minutes before departure and, if needed, before meals and at bedtime.

... Do not take more or less of it or take it more often than prescribed by your doctor or directed on the label.

Contraindicated in hypersensitivity. Caution in glaucoma, urinary retention, GI obstruction, liver or kidney disease, chronic obstructive pulmonary disease (COPD), seizure disorder.

Not recommended in infants or neonates.

Additive effects with alcohol and other CNS depressants, anticholinergics, some antidepressants (e.g., tricyclic antidepressants) and use of more than one antihistamine. Antihistamine effects may be potentiated by monamine oxidase inhibitors. Antacids may impair absorption of antihistamines.

Caution when operating machinery, driving a car, or engaging in underwater sports. Take with food or milk to reduce nausea.

FDA Pregnancy category B.