Preventer Inhalers for Asthma: What They Are and Why You Must Take Them Daily
What a preventer inhaler does, how inhaled steroids work, how long they take, the types used in the UK, side effects, and why stopping is risky.
Part of our asthma guide: symptoms, triggers and treatment.
Asthma attack? Get help now. Call 999 if your reliever isn’t helping, you’re too breathless to speak, eat or sleep, your breathing is getting faster, or your lips or fingertips are turning blue or grey. While you wait, sit up straight and take 1 puff of your blue reliever every 30 to 60 seconds, up to 10 puffs, through a spacer if you have one. If the ambulance hasn’t arrived after 10 minutes, repeat. Don’t complete an online consultation in an emergency.
Quick answer: A preventer inhaler contains an inhaled steroid (corticosteroid) that calms the inflammation in your airways. It’s taken every day, even when you feel well, and it doesn’t relieve sudden symptoms. It usually starts to help within a week or two, with the full effect over a few weeks. Stopping it lets inflammation build up again and raises your risk of an attack, so don’t stop without advice.
Already prescribed a preventer? See all our asthma inhalers online.
Order Your Usual Preventer Inhaler
Access Doctor is a GPhC-registered pharmacy (#9011198). If you’re an adult with diagnosed asthma or COPD, a pharmacist independent prescriber reviews your online consultation and supplies your usual inhaler if it’s safe, and we let your GP know. Approved before 3pm, Monday to Friday? Dispatched the same day, by Royal Mail Tracked 48, Tracked 24 or Special Delivery guaranteed by 1pm next working day: you choose. Delivery is free on orders over £40.
Start Asthma Consultation →Who our online service is for. Access Doctor supplies asthma and COPD inhalers to adults aged 18 and over who already have a diagnosis, for the same inhaler, strength and dose they’re prescribed now, and we share the consultation with your GP. We can’t diagnose asthma or start or change treatment online. Children’s inhalers are managed by their GP or asthma nurse.
Preventer inhalers are one of the most important asthma treatments, yet many people use them less than prescribed, often relying on their blue reliever instead. This guide explains what preventers are, how they work, why daily use matters, and what happens if you stop. For every type of inhaler, see our asthma inhalers guide; for one specific preventer, see our Clenil Modulite guide.
What Is a Preventer Inhaler?
A preventer inhaler contains an inhaled corticosteroid (ICS), a steroid medicine that works inside the airways to reduce long-term inflammation, cut mucus production and make the airways less likely to overreact to triggers.
How it differs from a reliever:
| Preventer inhaler (ICS) | Reliever inhaler (SABA) | |
|---|---|---|
| What it does | Reduces airway inflammation over time | Opens the airways quickly |
| How fast | Days to weeks of daily use | Within about 5 minutes |
| For sudden symptoms? | No | Yes |
| When to take it | Every day, at the same times, even when well | When you have symptoms, or before exercise if advised |
| Can you stop it? | Not without advice: inflammation builds up again | Used only when needed |
| Usual colour | Often brown or orange (colours vary by brand) | Blue |
How Do Inhaled Corticosteroids Work?
Breathed in every day, the steroid acts on the cells lining the airways. Over time it:
- reduces the chemical signals that drive inflammation in the airway lining
- lowers the number of eosinophils, the inflammatory cells involved in much asthma
- reduces swelling and excess mucus
- makes the airways less likely to overreact to triggers
Taken regularly, inhaled steroids reduce symptoms, the need for a reliever, and the risk of asthma attacks. They’re the foundation of asthma treatment in UK guidance.
Why Must I Take My Preventer Every Day?
The inflammation in asthma is there all the time, even between flare-ups when you feel completely well. If you miss doses, it builds back up gradually, often without symptoms at first, while your airways become more reactive over days and weeks.
The riskiest pattern in asthma is relying on a reliever while using little or no preventer, which is exactly what happens when people stop their preventer because they “feel fine”. The UK’s National Review of Asthma Deaths found that many people who died had been using too many relievers and too few preventers, and UK guidance treats high reliever use as a warning sign.
Warning sign: if you need your reliever more than twice a week, wake at night with asthma, or have used 3 or more reliever inhalers in a year, your asthma isn’t controlled. Contact your GP or asthma nurse for a review.
How Long Before a Preventer Inhaler Works?
A preventer works gradually:
- First few days: the anti-inflammatory effect starts, but you may not notice a difference yet. Keep using your reliever when you need it.
- Within a week or two: most people start to notice fewer symptoms and need their reliever less.
- Over the next few weeks: the full effect builds with daily use, with better control and fewer attacks.
If your symptoms haven’t improved after a few weeks of daily use with good technique, see your GP or asthma nurse. Your technique may need correcting, the dose may need changing, or a different inhaler, such as a combination inhaler, may suit you better.
Types of Preventer Inhaler Available in the UK
| Inhaler | Inhaled steroid | Strengths (per puff) | Low daily dose* | Device |
|---|---|---|---|---|
| Clenil Modulite | Beclometasone (standard particles) | 100, 200mcg (50 and 250mcg ending November 2026) | 200 to 500mcg | Aerosol (brown); use with a spacer |
| Qvar | Beclometasone (extra-fine) | 50, 100mcg | 100 to 200mcg | Autohaler, Easi-Breathe or aerosol. About twice as strong as Clenil |
| Flixotide | Fluticasone propionate | 50 to 500mcg | 100 to 250mcg | Aerosol (orange) or Accuhaler |
| Pulmicort | Budesonide | 100, 200, 400mcg | 200 to 400mcg | Turbohaler (dry powder) |
*Daily dose ranges from the NICE, BTS and SIGN (NG245) inhaled steroid dose tables, for people aged 12 and over. They’re a guide to similar effect, not exact equivalents.
All work well at the right dose. The choice depends on your symptoms, the device you can use best, and what UK guidance recommends at your stage of treatment. Beclometasone inhalers aren’t interchangeable: Clenil and Qvar contain the same steroid, but Qvar’s finer particles make it about twice as strong, so they’re prescribed by brand. Access Doctor supplies the preventer you’re already prescribed, at the same strength and dose; we can’t switch brands online.
Preventer · Rx
Clenil Modulite
Beclometasone aerosol, the brown preventer. 100 and 200mcg (50 and 250mcg ending November 2026).
View product →Preventer · Rx
Qvar Autohaler
Extra-fine beclometasone; fires as you breathe in. 50 and 100mcg.
View product →Preventer · Rx
Pulmicort Turbohaler
Budesonide dry powder inhaler. 100, 200 and 400mcg.
View product →Combination · Rx
Symbicort Turbohaler
Steroid and formoterol in one; daily, or as AIR or MART.
View product →Combination Inhalers, AIR and MART
Many people take their inhaled steroid in a combination inhaler, which also contains a long-acting bronchodilator (LABA), such as Symbicort, Fostair or Seretide. Purple and red inhalers are usually combination inhalers.
Since November 2024, UK guidance (NICE, BTS and SIGN, NG245) starts most adults on a combination inhaler containing a low-dose steroid and formoterol, rather than a steroid-only preventer plus a blue reliever:
- AIR (anti-inflammatory reliever): used only when you have symptoms, so every dose for symptoms also gives steroid
- MART (maintenance and reliever therapy): taken every day, plus extra doses when you have symptoms
If your asthma is well controlled on a steroid-only preventer and a separate reliever, you don’t have to switch, but you can ask about AIR or MART at your next review. Our asthma inhalers guide explains how they work.
How to Take Your Preventer
- Same times every day: most preventers are taken twice a day, morning and evening. Linking it to brushing your teeth helps you remember.
- Use a spacer with an aerosol preventer such as Clenil Modulite. It gets more medicine into your lungs and less in your mouth; the Clenil product information says a spacer must be used at doses of 1,000 micrograms a day or more.
- Rinse your mouth and spit after each dose, to lower the risk of thrush and a hoarse voice.
- Check your technique: ask a pharmacist or asthma nurse to watch you use it. See our guide to how to use an asthma inhaler.
- In an attack, use your reliever, not a steroid-only preventer. Call 999 if your reliever isn’t helping.
Side Effects of Preventer Inhalers
In the mouth and throat
- Oral thrush: white patches or soreness in the mouth. Rinsing your mouth after each dose and using a spacer greatly reduce the risk. If you get it, see our oral thrush treatment page or ask a pharmacist.
- Hoarse voice: usually improves with rinsing, a spacer and better technique.
At high doses over a long time
At low and moderate doses, effects on the rest of the body are rarely significant for adults. At high doses (for example more than 1,000 micrograms a day of Clenil, or the equivalent) over a long time, effects can include adrenal suppression, thinner bones, and cataracts or glaucoma; in children, growth can be slightly slowed. That’s why your prescriber aims for the lowest dose that controls your asthma and reduces it when your asthma has been well controlled.
Steroid emergency card: if you use a high dose of an inhaled steroid, or have recently taken steroid tablets, you may need to carry a steroid emergency card so that any doctor treating you in an emergency knows. Ask your GP or pharmacist if you’re not sure.
Get help straight away if your wheeze or breathlessness gets suddenly worse straight after a dose (use your reliever and call 999 or NHS 111), or you get swelling of the face, lips or throat (call 999).
The balance is clear: the risks of poorly controlled asthma are far greater than the risks of a preventer at the dose you need.
What Happens If I Stop My Preventer?
After stopping a preventer, inflammation in the airways builds back up gradually. At first you may notice no change. Over the following weeks the airways become more reactive, symptoms return, you need your reliever more, and a trigger such as a cold is more likely to cause a severe attack. Many hospital admissions for asthma follow a period of not taking a preventer.
If cost, side effects or anything else is making you think about stopping, talk to your GP, asthma nurse or pharmacist; there’s usually an alternative. Don’t stop without advice.
Getting Your Preventer Inhaler Online
Can you buy a preventer inhaler over the counter? No. Preventer inhalers are prescription-only medicines in the UK, so no pharmacy can sell one without a prescriber checking it’s right for you, in person or online. Access Doctor is a GPhC-registered pharmacy (registration number 9011198). If you’re an adult with diagnosed asthma, you can order the same preventer you already use, at the same strength and dose, after an online consultation. A pharmacist independent prescriber checks it’s safe, and we share the consultation with your GP. Approved before 3pm, Monday to Friday? Dispatched the same day, by Royal Mail Tracked 48, Tracked 24 or Special Delivery guaranteed by 1pm next working day: you choose. Delivery is free on orders over £40.
See our guide to ordering an asthma inhaler online for how the service works, or go straight to all our asthma inhalers online.
Safety, your GP and free NHS options
Preventers and other asthma inhalers are prescription-only medicines in the UK. Before anything is supplied, a GPhC-registered pharmacist independent prescriber reviews your consultation, including the other medicines you take; some, such as beta-blockers, can make asthma worse.
- Relievers on their own: since 2024, UK guidance (NICE, BTS and SIGN) says no one with asthma should be treated with a reliever alone, and in April 2025 the MHRA told prescribers not to prescribe one without an inhaled steroid to people of any age with asthma. If you don’t use a preventer, we can supply a reliever once and will ask you to see your GP or asthma nurse.
- How many: up to 2 reliever inhalers per order. If you’ve needed 3 or more in the last 12 months, we’ll ask you to have an asthma review first; needing that many is linked to a higher risk of severe attacks.
- Read the leaflet in the pack, and ask a pharmacist or asthma nurse to check your technique.
- Report side effects to a pharmacist or doctor. You can also report them to the MHRA through the Yellow Card scheme.
We share your consultation with your GP because asthma needs ongoing care. Access Doctor is a private service, and there are free NHS options:
- Your GP practice: asthma reviews (at least once a year) and repeat prescriptions; many practices let you order repeats through the NHS App.
- Prescription charges: NHS prescriptions are free in Scotland, Wales and Northern Ireland. In England a charge applies unless you’re exempt, and a prepayment certificate can save money if you need several items.
- Urgent advice: NHS 111 (NHS 24 on 111 in Scotland), or 999 in an emergency.
Need Your Usual Inhaler?
Access Doctor is a GPhC-registered pharmacy (#9011198). If you’re an adult with diagnosed asthma or COPD, a pharmacist independent prescriber reviews your online consultation and supplies your usual inhaler if it’s safe, and we let your GP know. Approved before 3pm, Monday to Friday? Dispatched the same day, by Royal Mail Tracked 48, Tracked 24 or Special Delivery guaranteed by 1pm next working day: you choose. Delivery is free on orders over £40.
Start Asthma Consultation →Frequently Asked Questions
Do I need to take my preventer inhaler every day?
Yes, unless your GP or asthma nurse has set it up differently. A preventer works by keeping the inflammation in your airways down, and that protection only lasts while you keep taking it. Take it every day, even when you feel well. If you miss doses, inflammation builds back up over days, your airways become more reactive, and your risk of an attack rises. The exception is a combination inhaler prescribed as AIR, which is used only when you have symptoms.
How long before a preventer inhaler works?
Most people start to notice a difference within a week or two, with the full effect building over a few weeks of daily use. Don’t stop because it doesn’t seem to work straight away. If your symptoms haven’t improved after a few weeks of taking it every day with good technique, see your GP or asthma nurse; your technique, dose or inhaler may need changing.
What happens if I stop my preventer inhaler?
The inflammation in your airways gradually builds back up over days to weeks, and your risk of symptoms and asthma attacks rises. The UK’s National Review of Asthma Deaths found that many people who died had been using too many reliever inhalers and too few preventers. Don’t stop without advice. If your asthma has been well controlled for at least 3 months, ask your GP or asthma nurse about reducing your dose at your review.
What is the difference between a preventer and a reliever inhaler?
A reliever (usually blue, such as Ventolin) opens the airways within minutes when you have symptoms, but doesn’t treat the inflammation. A preventer contains an inhaled steroid that reduces inflammation when taken every day, even when you feel well; it doesn’t give quick relief. Preventers are often brown (such as Clenil Modulite) or orange; purple and red inhalers are usually combination inhalers. Needing your reliever more than twice a week means your treatment needs a review. Our asthma inhalers guide explains each type.
Can I stop my preventer in summer when my asthma is better?
No. Feeling better is usually a sign the preventer is working, and stopping it removes that protection. Many people’s asthma gets worse in autumn, when colds and mould spores rise, especially around September, so stopping over the summer leaves you less protected just before then. Talk to your GP or asthma nurse before changing your treatment. See our autumn asthma guide.
Are preventer inhalers safe long-term?
Yes, at the doses most adults need. Because the steroid is breathed straight into the airways, only a small amount reaches the rest of the body, much less than with steroid tablets. At high doses over many years, effects on the adrenal glands, bones and eyes are possible, which is why your prescriber aims for the lowest dose that keeps your asthma controlled. The risks of poorly controlled asthma (attacks, hospital admission and, rarely, death) are far greater.
What colour is a preventer inhaler?
Many preventers are brown, such as Clenil Modulite and Pulmicort Turbohaler, and Flixotide is orange. There’s no UK colour standard, though, and the same medicine can come in a different colour from another maker. Always check the name and strength on the label. Our asthma inhalers guide explains what each colour usually means.
Is a combination inhaler a preventer?
Yes. A combination inhaler, such as Symbicort, Fostair or Seretide, contains an inhaled steroid (the preventer part) and a long-acting bronchodilator. Under UK guidance since 2024, most adults are started on a steroid-and-formoterol combination inhaler rather than a steroid-only preventer, used when needed (AIR) or every day plus extra doses (MART).
For symptoms, triggers and how asthma is diagnosed, see our asthma guide.
References
- NICE, BTS and SIGN. Asthma: diagnosis, monitoring and chronic asthma management (NG245), November 2024. nice.org.uk
- NICE, BTS and SIGN. Asthma: inhaled corticosteroid doses for people aged 12 and over (NG245 dose tables), November 2025. sign.ac.uk
- MHRA Drug Safety Update. Short-acting beta-2 agonists (SABA): reminder of the risks from overuse in asthma and changes in the SABA prescribing guidelines, April 2025. gov.uk
- Electronic Medicines Compendium. Clenil Modulite: Summary of Product Characteristics. medicines.org.uk
- Royal College of Physicians. Why asthma still kills: the National Review of Asthma Deaths, 2014. rcp.ac.uk
- NHS. Asthma: treatment. nhs.uk
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional for diagnosis and treatment. In a medical emergency, call 999.