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Dosage varies with drug, patient and intended use. Consult more detailed references for further information.
When used for control of allergic reactions, antihistamines should be taken on a regular schedule, rather than on an as-needed basis, since they have no effect on histamine itself, nor on histamine already bound to the receptor site.
Efficacy is highly variable from patient to patient. If an antihistamine fails to provide adequate relief, switch to a drug from a different chemical class. Individual drugs may be effective in no more than 40% of patients, and provide 50% relief of allergic symptoms.
| Antihistamines | |
| Brand Name (Generic Name) | Possible Common Side Effects Include: |
| *Also used in the treatment of anxiety | |
| *Atarax (hydroxyzine hydrochloride) | Drowsiness, dry mouth |
| Benadryl (diphenhydramine hydrochloride) | Dizziness, sleepiness, upset stomach, decreased coordination |
| Hismanal (astemiozole) | Drowsiness, dry mouth, fatigue, weight gain |
| PBZ-SR (tripelennamine hydrochloride) | Dizziness, drowsiness, dry mouth and throat, chest congestion, decreased coordination, upset stomach |
| Periactin (cyproheptadine hydrochloride) | Chest congestion, dizziness, fluttery heartbeat, loss of appetite, hives, sleepiness, vision problems |
| Phenergan (promethazine hydrochloride) | Changes in blood pressure, dizziness, blurred vision, nausea, rash |
| Polaramine (dexchlorpheniramine maleate) | Drowiness |
| Seldane, Seldane-D (terfenadine) | Upset stomach, nausea, drowiness, headache, fatigue |
| Tavist (clemastine fumarate) | Decreased coordination, dizziness, upset stomach |
| Trinalin Repetabs (azatadine maleate, pseudoephedrine sulfate) | Abdominal cramps, chest pain, dry mouth, headache |
— Samuel Uretsky, PharmD
