Montelukast is a leukotriene receptor antagonist. Rather than blocking histamine, it blocks leukotrienes — different inflammatory messengers involved in the allergic response. It is taken as a daily tablet.
It is best known as an asthma medicine, but it is also used for allergic rhinitis, particularly where hay fever and asthma coexist, since one tablet addresses both.
Where It Fits
Montelukast is not a first-line hay fever treatment. The usual sequence is an antihistamine, then a steroid nasal spray, then a combination. Montelukast tends to be considered when:
- You have asthma as well as hay fever, and both worsen in pollen season
- Standard treatments have not given adequate control
- Nasal sprays are not tolerated or not used reliably
On its own it is generally less effective for nasal symptoms than a steroid nasal spray.
The Safety Warnings
Following a review, the MHRA concluded that the risk of neuropsychiatric reactions with montelukast had not changed but was not well enough known by prescribers, patients or carers. It required more prominent warnings, highlighted with a boxed warning, in the patient information leaflet of every UK montelukast product.
Reported reactions include:
- Sleep disorders, including insomnia and vivid or disturbing dreams
- Depression and anxiety
- Agitation and behaviour changes
- More rarely: hallucinations, memory disturbance and suicidal thoughts
Reading the Numbers Fairly
Since montelukast was authorised in the UK in 1998, around 44 million prescriptions have been issued, with 1,223 reports of suspected neuropsychiatric adverse reactions.
Yellow Card reports are suspected, not confirmed, and voluntary reporting undercounts. But even generously interpreted, this is a rare effect rather than a common one, and the MHRA's conclusion was that benefits continue to outweigh risks for most patients.
The reason for the warnings is not that the risk is large. It is that when it happens, the person affected — or their parents — need to recognise it as a possible medication effect rather than something else entirely.
What to Watch For
Changes in mood, sleep or behaviour after starting montelukast should be reported to a prescriber. In children this is particularly important, because a child is unlikely to make the connection themselves, and the change may present as irritability, nightmares or a shift in behaviour rather than as anything a child would describe as low mood.
Seek medical advice promptly rather than waiting to see whether it settles, and report it through the Yellow Card scheme.
Weighing It Up
Montelukast helps a great many people, particularly those with both asthma and hay fever. The question is whether it is the right rung of the ladder for you — and for hay fever alone, when a steroid nasal spray has not been given a fair trial with correct technique, it usually is not.
If you are already taking it and doing well, these warnings are not a reason to stop. They are a reason to know what to look for, and to say something if you see it.