Singulair (montelukast) is a widely prescribed asthma allergy medication used to manage asthma and allergic rhinitis in both adults and children across the UK. As a leukotriene receptor antagonist (LTRA), it works differently from inhalers and antihistamines, blocking the chemical messengers that drive airway inflammation and allergic symptoms. Whether you have been newly prescribed montelukast or are reviewing your current treatment, understanding how it works, who it is suitable for, and its important safety considerations — including the MHRA mental health warning — is essential for safe and effective use.

What Is Singulair and How Does It Work?

Singulair is a brand name for montelukast, a prescription medicine classified as a leukotriene receptor antagonist (LTRA). It works by blocking the action of leukotrienes — naturally occurring chemical messengers released by the immune system in response to allergens, exercise, or irritants. In people with asthma or allergic conditions, leukotrienes contribute to:

• Airway inflammation and swelling

• Bronchoconstriction (narrowing of the airways)

• Increased mucus production

• Nasal congestion and sneezing in allergic rhinitis

By selectively blocking the cysteinyl leukotriene receptor (CysLT1), montelukast reduces leukotriene-mediated bronchoconstriction and inflammation. It is a distinct class of medicine from inhaled corticosteroids (ICS) and does not replace ICS when these are clinically indicated. Unlike inhaled bronchodilators, Singulair is taken orally and works over a sustained period rather than providing immediate symptom relief. It is therefore considered a preventer or controller medicine, not a rescue treatment.

Montelukast has been licensed in the UK since the late 1990s and is widely used in both adults and children. It is available as a generic medicine under the name montelukast, with Singulair being the original branded formulation manufactured by MSD (Merck Sharp & Dohme). Licensed generic versions are bioequivalent to the brand, as demonstrated through the UK licensing process. Understanding how the drug works helps patients appreciate why consistent daily use — rather than on-demand dosing — is essential for achieving its full therapeutic benefit.

References: MHRA/EMC SmPC — Montelukast (all formulations); NHS medicines page: Montelukast.

Approved Uses for Asthma and Allergic Rhinitis in the UK

In the UK, montelukast (Singulair) is licensed across several formulations for two principal indications. Prescribing decisions should always be made in consultation with a qualified healthcare professional.

1. Asthma Montelukast is licensed as add-on therapy for adults and children aged 6 months and over whose asthma is not adequately controlled by inhaled corticosteroids (ICS) alone, or as an alternative to a low-dose ICS in mild persistent asthma where ICS are not suitable. According to NICE guideline NG245 (Asthma: diagnosis and management), LTRAs such as montelukast may be considered as part of the asthma management pathway, particularly in patients who are unable or unwilling to use inhaled therapy, or where an ICS plus LTRA combination is being considered before stepping up to ICS plus long-acting beta-agonist (LABA). Clinicians should refer to current NICE guidance for the precise positioning of LTRAs within the treatment algorithm.

Montelukast may also be considered in clinical practice for exercise-induced bronchoconstriction and in patients whose asthma is triggered by aspirin or non-steroidal anti-inflammatory drugs (NSAIDs); however, these are not separately listed as distinct licensed indications in all UK SmPCs, and use in these contexts should be guided by a clinician.

2. Allergic Rhinitis The licensed indications for allergic rhinitis vary by formulation and age group, as specified in the UK SmPCs:

• 10 mg film-coated tablets (adults and adolescents aged 15 years and over): licensed for relief of symptoms of seasonal allergic rhinitis (SAR) in patients who also have asthma for whom montelukast is indicated for asthma.

• 5 mg chewable tablets (children aged 6–14 years): licensed for relief of symptoms of seasonal allergic rhinitis in patients who also have asthma.

Montelukast is not licensed in the UK for perennial allergic rhinitis, and is not licensed for SAR in children under 6 years. It is particularly useful when seasonal allergic rhinitis coexists with asthma, as it can address both conditions with a single oral dose.

It is important to note that montelukast is not a first-line treatment for allergic rhinitis. NICE and NHS guidance generally recommend intranasal corticosteroids and non-sedating antihistamines as initial therapy. Montelukast tends to be considered when these options are insufficient or poorly tolerated, and always within its licensed indications.

References: MHRA/EMC SmPCs — Montelukast 10 mg film-coated tablets, 5 mg chewable tablets, 4 mg chewable tablets, 4 mg granules; NICE NG245: Asthma: diagnosis and management; BNF/BNFc: Montelukast monograph.

How to Take Singulair: Doses, Forms, and Timing

Singulair and generic montelukast are available in several formulations to accommodate different age groups and clinical needs:

• 4 mg oral granule sachets — for infants and young children aged 6 months to 5 years

• 4 mg chewable tablets — for children aged 2 to 5 years

• 5 mg chewable tablets — for children aged 6 to 14 years

• 10 mg film-coated tablets — for adults and adolescents aged 15 years and over

Dosing frequency: Montelukast is taken once daily. For asthma management, it should be taken in the evening, as leukotriene levels tend to peak overnight and in the early morning — the period when asthma symptoms are often at their worst. For isolated seasonal allergic rhinitis, timing may be individualised, though consistency is important.

Food and administration guidance:

• Chewable tablets (4 mg and 5 mg): should be taken at least 1 hour before or 2 hours after food.

• 10 mg film-coated tablets: may be taken with or without food.

• 4 mg granule sachets: administer the granules directly into the mouth, or mix with a small amount (one teaspoon) of cold or room-temperature soft food such as apple purée. Do not dissolve granules in any liquid. Once mixed, the preparation must be used immediately (within 15 minutes) and must not be stored.

Key patient safety points:

• Do not use Singulair as a rescue inhaler during an acute asthma attack — continue to use your reliever inhaler as prescribed.

• If you miss a dose, take it as soon as you remember on the same day; do not double up the following day.

• Always inform your GP or pharmacist of all other medicines you are taking. Certain medicines that induce liver enzymes — including rifampicin, phenytoin, and phenobarbital — may reduce montelukast's effectiveness. Conversely, gemfibrozil may increase montelukast exposure. This list is not exhaustive; always seek advice from your prescriber or pharmacist.

• Patients should not stop taking montelukast without first consulting their GP, even if symptoms appear to have resolved.

References: MHRA/EMC SmPCs — Montelukast 4 mg granules, 4 mg chewable tablets, 5 mg chewable tablets, 10 mg film-coated tablets; NHS medicines page: Montelukast.

Side Effects and the MHRA Mental Health Warning

Montelukast is generally well tolerated, but like all medicines, it can cause side effects. Common side effects include:

Experiencing these side effects? Our pharmacists can help you navigate them →

• Headache (particularly in adults)

• Abdominal pain, nausea, or diarrhoea

• Upper respiratory tract infections

• Increased thirst and mild fever in younger children

These effects are usually mild and transient. However, the most significant safety concern relates to neuropsychiatric side effects, which prompted a formal regulatory review and updated guidance from both the MHRA and the EMA.

MHRA Mental Health Warning Following a review of post-marketing safety data, the MHRA has required that the patient information leaflet and Summary of Product Characteristics (SmPC) for all montelukast products carry a prominent warning about neuropsychiatric reactions. These may include:

• Agitation, aggression, or irritability

• Anxiety and depression

• Sleep disturbances, including nightmares, insomnia, and abnormal dreams

• Suicidal thoughts and behaviour (rare but serious)

• Hallucinations, tremor, attention disturbances, and tics

These effects have been reported across all age groups but appear to occur more frequently in children and adolescents. Whilst a causal relationship between montelukast and these neuropsychiatric events — including suicidal thoughts and behaviour — has not been definitively established, the events have been reported in post-marketing data and warrant careful attention. Caution and prompt medical advice are essential.

Rare but important warning — eosinophilia and EGPA: In rare cases, patients taking montelukast (particularly those whose oral corticosteroid dose is being reduced) have developed systemic eosinophilia or features consistent with eosinophilic granulomatosis with polyangiitis (EGPA). Seek urgent medical review if you develop symptoms such as a new or worsening rash, worsening breathing, numbness or tingling in the limbs, or other unexplained symptoms.

When to seek medical advice:

• Contact your GP promptly if you or your child experiences mood changes, unusual behaviour, sleep problems, or any thoughts of self-harm while taking montelukast.

• Seek urgent medical attention if symptoms are severe, including any thoughts of suicide or self-harm, or if you develop symptoms that may suggest EGPA.

• Do not stop the medication abruptly without medical guidance, but do seek urgent advice if symptoms are severe.

The MHRA advises that prescribers should discuss these risks with patients and carers before starting treatment, and that the benefits and risks should be reviewed regularly. Patients and carers are encouraged to report any suspected side effects via the Yellow Card scheme at yellowcard.mhra.gov.uk.

References: MHRA Drug Safety Update (2022): Montelukast — reminder of the risk of neuropsychiatric reactions; MHRA/EMC SmPC: Montelukast (Undesirable effects, Special warnings and precautions for use); EMA PRAC communications on montelukast neuropsychiatric safety.

Frequently Asked Questions