Patients frequently report side effects related to the nervous system, such as sedation, drowsiness and depression, after using diphenhydramine hydrochloride, states Drugs.com. Other dangers include dystonic reactions, delirium and hypersensitivity, such as eczema, pruritus and rash.
Patients with conditions such as liver or kidney disease, chronic obstructive pulmonary disease, thyroid disorders, or blockage in the digestive tract should consult their doctors before taking diphenhydramine hydrochloride, warns Drugs.com. Patients should seek immediate health care if they experience difficulty urinating, irregular or fast heartbeat, and mood changes, such as confusion and restlessness, after they take this medication, advises WebMD. Children and older people can be more sensitive to the side effects, and women should consult their doctors before breast-feeding, as this drug can pass into breast milk.