All medications can cause side effects, but most hay fever treatments are well tolerated by the vast majority of people. Understanding what to expect can help you make informed decisions and know when to seek advice from a pharmacist or GP.
Antihistamine Side Effects
Second-Generation (Non-Drowsy) Antihistamines
These include cetirizine, loratadine, and fexofenadine — the most commonly used hay fever tablets in the UK.
- Drowsiness: Fexofenadine is the least likely to cause drowsiness. Cetirizine may cause mild sleepiness in up to 10% of users. Loratadine sits in between.
- Headache: Reported by a small number of users across all three medications
- Dry mouth: More common with cetirizine
- Stomach upset: Rare, but can occur with any antihistamine
First-Generation (Sedating) Antihistamines
Chlorphenamine (Piriton) is still available in the UK. It is effective but causes significant drowsiness in many users. The MHRA advises against driving while taking chlorphenamine. Other side effects include blurred vision, difficulty urinating, and dry mouth.
Steroid Nasal Spray Side Effects
Corticosteroid nasal sprays are considered very safe for long-term use at recommended doses. Possible side effects include:
- Nosebleeds: The most common side effect, reported by around 5–10% of users. Often caused by incorrect spray technique — aim away from the septum to reduce risk.
- Nasal dryness or irritation: Usually mild and temporary
- Sore throat: Occasionally reported
- Headache: Uncommon
Systemic side effects (those affecting the whole body) are extremely rare with nasal steroids at standard doses, unlike oral steroids.
Eye Drop Side Effects
Antihistamine eye drops such as sodium cromoglicate (Opticrom) and olopatadine may cause:
- Temporary stinging or burning on application
- Mild blurred vision lasting a few minutes
- Eye dryness with prolonged use
When to See Your GP
Most side effects are mild and resolve on their own. However, you should contact your GP or pharmacist if you experience:
- Persistent nosebleeds that do not stop with technique adjustment
- A rash, swelling, or breathing difficulty (signs of a rare allergic reaction)
- Drowsiness that affects your daily activities or driving
- Any side effect that concerns you or persists beyond a few days
Your pharmacist can help you switch to an alternative medication if side effects are bothersome.