Antihistamines: Findings in Clinical Trials Relevant to Therapeutics

Antihistamine therapy reduces hay fever symptoms 50–60% within 5 hours after the first dose. Treatment for 9 days maintains but does not reduce symptoms further. Patients treated with placebo for 8 days and then treated with chlorpheniramine obtained as much relief by the 5th hour after treatment as those treated with chlorpheniramine for 9 days. Increasing the dose of any antihistamine we tested over that necessary for maximal relief produces no greater benefit. Antihistamine treatment doses currently recommended may be greater than necessary for most patients. Antihistamines do not reduce nasal congestion and are not decongestants.