In short: Allergen immunotherapy (desensitisation) is the only hay fever treatment that targets the allergy itself rather than just the symptoms. It involves regular, controlled doses of the pollen you are allergic to, usually as a daily tablet under the tongue or as a course of injections, given under specialist supervision for around three years. It is reserved for people with significant hay fever that is not controlled by standard treatments.

This guide, written by a Ready Health prescribing pharmacist, explains how immunotherapy works and who it may be suitable for.

What is allergen immunotherapy?

Immunotherapy gradually trains the immune system to become less reactive to a specific allergen, such as grass or tree pollen. Over time this can reduce symptoms and the need for other medicines, and benefits may continue for some years after a full course. Because treatment carries a small risk of allergic reactions, it should only be started by an allergy specialist.

Who might be suitable for immunotherapy?

Immunotherapy may be considered if:

your hay fever is clearly linked to a specific pollen, confirmed by your history and allergy testing
symptoms remain troublesome despite correctly using steroid nasal sprays, antihistamines and eye drops
hay fever significantly affects your sleep, work, studies or quality of life
you are able to commit to treatment for around three years

It is usually not suitable if you have severe or poorly controlled asthma, some immune system conditions or active cancer, and it is not started during pregnancy.

How is immunotherapy given?

	Tablet under the tongue (sublingual)	Injections (subcutaneous)
How often	Daily, at home after the first dose	Regular injections in a specialist clinic
Supervision	First dose in clinic with observation	Each injection given in clinic with a period of observation afterwards
When to start	Usually two to four months before the pollen season	Before the season, following a specialist schedule
Typical length	About three years	About three years

Immunotherapy injections contain tiny amounts of allergen and are completely different from long-acting steroid injections. For clarity, long-acting steroid injections are not licensed for hay fever in the UK and are not recommended in UK guidance, because they act on the whole body for weeks and can cause dents in the skin at the injection site, raised blood sugar, mood and sleep changes, suppression of the body's own steroid hormones and, with repeat use, bone thinning.

What are the side effects of immunotherapy?

With under-the-tongue tablets, the most common side effects occur in the first week or two and include itching or mild swelling in the mouth, throat irritation and sometimes stomach upset. With injections, redness and swelling at the injection site are common. Serious allergic reactions are uncommon but possible, which is why the first dose (and each injection) is given under supervision. Seek emergency help for breathing difficulty, throat tightness or swelling of the face, lips or tongue.

How do I get referred for immunotherapy?

In the NHS, a GP can refer you to an allergy service if your hay fever is severe and not controlled by optimal treatment. Availability varies by area, and the specialist team will confirm the diagnosis, often with skin prick or blood tests, before deciding whether immunotherapy is appropriate. A private prescriber can also review your treatment and, where appropriate, write to your GP to support a referral.

Frequently asked questions

How long before immunotherapy starts to work?

Some people notice benefit in the first season, but the full effect builds over the course of treatment. If there is no improvement after about a year, the specialist team will review whether to continue.

Can I keep using my usual hay fever medicines?

Yes. Continue your usual treatments unless your specialist advises otherwise.

Can children have immunotherapy?

Yes, some forms are used in children from around five years old, under the care of a paediatric allergy specialist.

Is immunotherapy a cure?

Not always, but a full course can reduce symptoms and medicine use for several years.

Key takeaways

Immunotherapy targets the allergy itself, not just the symptoms.
It is a specialist treatment for significant hay fever not controlled by standard medicines.
Treatment usually lasts around three years and starts months before the pollen season.
The first dose, or each injection, is given under supervision because of a small risk of allergic reaction.
Your GP can refer you to an allergy service if appropriate.

Sources and further reading

Last reviewed: October 2026 by Shamir Patel, Independent Prescribing Pharmacist, Ready Health. This article is general information and does not replace advice from your own clinician.

If your hay fever is not controlled and you would like to discuss next steps, including whether specialist referral might be appropriate, you can book a hay fever consultation at Ready Health in Standish, Wigan. A prescriber will review your symptoms and treatment and explain suitable options. Any prescription is only issued if a prescriber decides it is clinically appropriate.

Hay Fever Immunotherapy: What You Need to Know