What should you know about diphenhydramine for a runny nose?

A runny nose can occur with allergic rhinitis, a common cold, influenza, COVID-19 or sinusitis. Diphenhydramine is an antihistamine, so it is more relevant when histamine is contributing to symptoms such as sneezing, itching and watery discharge. It does not treat a viral infection or clear a blocked sinus. It may cause sleepiness, dry mouth, blurred vision and reduced coordination. Read more about Runny Nose and Allergic Rhinitis.

Check the active ingredient and follow the product directions. Avoid driving, cycling, alcohol and other sedating medicines until you know how it affects you. Ask a pharmacist before use if you are pregnant, breastfeeding, older, have glaucoma, breathing problems, difficulty passing urine or take regular medicines. Saline rinsing, fluids and avoiding a known allergen may help depending on the cause. Do not combine several cold or allergy products without checking their ingredients.

Seek urgent help for trouble breathing, swelling of the lips or tongue, fainting, severe wheezing, confusion or a rapidly worsening allergic reaction. Arrange medical advice when a runny nose is accompanied by severe facial pain, persistent high fever, dehydration, chest symptoms, or symptoms that are worsening rather than settling. COVID-19 or influenza symptoms may need specific guidance for people at higher risk.

Ask whether the pattern fits allergy, infection or sinusitis, whether a less sedating option is preferable, and how long to try treatment. Take the packaging and a list of current medicines to the consultation.