Side effects and advice
Grazax hay fever treatment
Side effects
Because you’re taking a small dose of grass pollen every day, you might get some of your usual allergy symptoms. This includes symptoms like a runny nose or watery eyes.
Common side effects
You might get other common side effects during your first week of treatment. These include:
- irritation in your throat
- an itchy or tingling mouth, usually under your tongue
- swelling in your lips, tongue or gums, near where the tablet dissolved
- itchy ears
- tummy pain
- feeling sick (nausea)
Read the leaflet inside your medicine package for a full list of side effects.
The side effects in your mouth usually appear within 5 minutes of taking the Grazax tablet. These side effects usually last for a few minutes, or a few hours.
You should get fewer side effects the longer you take Grazax. This means your body is building up tolerance to grass pollen.
If any of these symptoms continue after the first week of treatment, you can take an antihistamine. Take an antihistamine at least 1 hour before you take your Grazax tablet.
Contact us if:
- your side effects are getting worse and antihistamines do not help
Serious side effects
There’s a risk that you could have a more serious allergic reaction to Grazax.
Stop taking Grazax and contact us if:
- it’s more difficult to breathe or swallow than usual
- your throat feels full
- your voice changes
- you feel dizzy
- you have a rash on your skin
- you have asthma that is getting worse
We’ll discuss if it’s safe for you to continue your treatment. Stop taking Grazax until we discuss this with you.
Call 999 or go to A&E now if:
- your face, mouth or throat suddenly become extremely swollen
- you're breathing very fast or struggling to breathe (you may become very wheezy or feel like you're choking or gasping for air)
- you suddenly become very confused, drowsy or dizzy
- you have a fast heartbeat
- you have an asthma attack
- you have fainted
These can be signs of a serious allergic reaction and may need immediate treatment in hospital. Stop taking Grazax immediately.
Taking other medicines
You can take most other medicines with Grazax safely. This includes your usual medicines for hay fever or asthma.
Before you start treatment, we’ll check to make sure that you can continue taking your medicines with Grazax.
Tell us if your medicines change after you have started treatment.
If you start taking any new medicines during your treatment, it’s important you tell your doctor that you’re taking Grazax.
Medical procedures and vaccines
You must tell your doctor or dentist that you take Grazax before you have any medical or dental procedures.
If you have dental surgery (for example, to remove a tooth), stop taking Grazax for 7 days afterwards. This gives time for the cavity (hole) to heal.
Always contact us for advice about stopping and restarting treatment.
If you get any vaccines (such as the flu vaccine), you can still take Grazax on the day of your vaccine.
Pregnancy and breastfeeding
There is limited evidence available about taking Grazax while pregnant. Because of this, we do not start Grazax treatment when you are pregnant.
If you get pregnant or think that you might be pregnant during your Grazax treatment, stop taking Grazax and contact us. We can discuss if you should continue your treatment.
There is also limited evidence about taking Grazax while breastfeeding. We do not expect Grazax to affect your baby through breast milk. Contact us for more advice if you start breastfeeding.
Resource number: 2344/VER4
Last reviewed: March 2026
Next review due: March 2029
