What should you know about H1 antihistamines?

Histamine is one of the chemicals released during an allergic response. H1 antihistamines reduce its effects, which may ease sneezing, a runny or blocked nose, itchy eyes, and an itchy throat. They treat symptoms rather than removing the trigger. Symptoms linked with allergic rhinitis, allergic conjunctivitis, pet allergy, or house dust mite allergy may therefore improve while you take the medicine.

Some H1 products can make you sleepy, slow reactions, dry your mouth, or blur your vision. Others are less sedating, although drowsiness can still occur. Alcohol, driving, machinery, and other medicines that cause sleepiness can increase the risk of impaired alertness.

Read the label and use the recommended dose; do not combine different antihistamines unless a clinician or pharmacist has specifically advised it. Check the active ingredient in multi-symptom cold products so you do not double up. A pharmacist can help you choose between a sedating and a less-sedating option for your pattern of symptoms.

Tell the pharmacist or clinician if you are pregnant, breastfeeding, treating a child, or have glaucoma, difficulty passing urine, liver or kidney disease, or a condition that affects heart rhythm. Seek advice before taking an antihistamine with sleeping tablets, calming medicines, or other treatments that may interact.

Get urgent help for swelling of the lips, tongue, or throat, trouble breathing, faintness, or rapidly spreading hives. An antihistamine is not a substitute for emergency treatment of a severe allergic reaction. Arrange medical advice if symptoms keep returning, disturb sleep, affect vision, or do not improve with appropriate use.

Ask which H1 antihistamine suits your symptoms, whether it may make you drowsy, how long to try it, and whether your current medicines or health conditions change the choice.