The drugs in the diphenhydramine class are mainly used to treat hypertension and can have certain side effects when taken for a long time, specifically the following adverse reactions: 1, when taking diphenhydramine drugs to lower blood pressure may cause swelling of the calves and ankles, which can be treated with diuretics to reduce swelling. 2, resulting in hypotension, when taking antihypertensive drugs for treatment, such as not regularly detecting blood pressure, adjusting the dosage of drugs may cause the blood pressure to drop too much, causing symptoms of hypotension. A small percentage of patients will have headache, chest pain, eye blossoms, palpitations and facial redness after taking diphenhydramine. 4, adverse reactions of the gastrointestinal tract, some patients will have diarrhea, abdominal pain, nausea, constipation and loss of appetite. 5, a small percentage of patients will have gum hypertrophy symptoms.