Diphenhydramine possesses a moderate degree of anticholinergic actions. Geriatric patients are more likely to experience such adverse reactions. Some of these adverse reactions may be relieved by taking the drug with meals or milk. Adverse cardiovascular responses are likely to be associated with the anticholinergic properties or the quinidine-like anesthetic effects of antihistamines. Alpha-adrenergic blockade can lead to symptoms of hypotension.
Hypertension can also occur.
Topically application of diphenhydramine can result in a hypersensitivity reaction. Allergic contact dermatitis has been reported and is manifested by inflammation, pruritus, and eczema. Generic diphenhydramine tablets or capsules are available, with or without a prescription. Take diphenhydramine tablets or capsules by mouth. Follow the directions on the prescription label.