Antihistamine Side Effect The Antihistamine Side Effect Guide You NEED! We often focus on the primary effects of drugs, but ignoring side effects can impact patient adherence and safety. Especially with antihistamines for common conditions like itching (pruritus) or allergies, understanding generations is key! First-Gen AH (e.g., Avil/Pheniramine, Atarax/Hydroxyzine, Diphenhydramine): 😴 Major Sedation ❤️ Tachyarrhythmias Dry mouth, constipation, urinary retention (Antimuscarinic effects) Second