Montelukast

Is montelukast safe?

Physically, it is one of the gentler medicines on our list: overdoses rarely cause symptoms, it barely interacts with other drugs and it is not addictive. The concern is the mind. Montelukast (Singulair) has carried a US boxed warningBoxed warningThe strongest safety warning the US FDA puts on a medicine's label, printed inside a black border at the top.More in the glossary since March 2020 for serious neuropsychiatric events, from nightmares and agitation to depression and, rarely, suicidal thoughts and behaviour.

That warning is why we score it 78, ten points below cetirizine, and why US labels now say it should not be a first choice for hay fever. For asthma, where it can reduce the need for steroids, the label asks doctors to weigh benefits and risks for each patient.

Doses on the US label are 10 mg once a day for ages 15 and over, a 5 mg chewable for 6 to 14, and 4 mg for 2 to 5 (chewable or granules), taken in the evening for asthma.

What are the mental health side effects of montelukast?

The label lists a wide range: agitation, aggression or hostility, anxiety, depression, disorientation, poor attention, abnormal dreams, stuttering, hallucinations, insomnia, irritability, memory problems, obsessive-compulsive symptoms, restlessness, sleep-walking, tics, tremor, and suicidal thoughts and behaviour, including suicide. They have been reported in children, teenagers and adults, with and without a psychiatric history, mostly during treatment but sometimes after stopping.

How often? The MHRA's 2024 review puts sleep disturbances, depression and agitation at up to 1 in 100 users, attention and memory problems at up to 1 in 1,000, and hallucinations and suicidal thinking at up to 1 in 10,000.

How strong is the evidence?

Mixed, which is part of why the warning is so prominent. The FDA's March 2020 review found 82 reports of completed suicide in its adverse event database, 19 of them in people aged 17 or under. Reports like these cannot prove cause, and many lacked detail, but the FDA judged the pattern serious enough for its strongest warning. Psychiatric warnings had been in the prescribing information since 2008, and the agency said many doctors and families still did not know about it.

Large studies point both ways:

Study	People	Finding
Sweden, JAMA Pediatrics 2025	74,291 children aged 6 to 17	No difference from a comparison asthma drug (hazard ratio 0.99)
US health records, Thorax 2024	107,384 children with asthma	71 vs 54 neuropsychiatric diagnoses per 1,000 (relative risk 1.32)

The honest summary: most children and adults take montelukast with no psychiatric effects, a minority have mood or sleep changes, and serious events are rare but real enough that regulators in the US, UK and Australia have all put the warning in a box.

What to watch for

The MHRA's advice is practical. Tell family and friends you or your child take montelukast, because people around you may notice changes before you do. Watch for nightmares, new sleep-walking, irritability, aggression, anxiety or low mood, especially in the first weeks. If any appear, the US label says to stop and contact a healthcare provider immediately.

Two other label warnings matter. Montelukast does not treat an asthma attack, so keep a rescue inhaler. And it should not suddenly replace inhaled or oral steroids; rare cases of a blood-vessel inflammation (eosinophilic granulomatosis, once called Churg-Strauss syndrome) have appeared as steroids were reduced. If a steroid such as prednisone is being cut back, that is a step for your doctor.

Overdose and interactions

Montelukast has a very wide margin. Adults have taken 200 mg a day for 22 weeks in asthma studies, and up to 900 mg a day for about a week, without clinically important harm. Most reported overdoses of up to 1,000 mg caused no symptoms; the rest mostly caused stomach pain, sleepiness, thirst, headache or vomiting. If a child swallows extra tablets, call Poison Help on 1-800-222-1222 in the US or NHS 111 in the UK.

The label lists no drugs that need a dose change, including theophylline, warfarin, digoxin, birth control pills and sedatives. The 4 mg and 5 mg chewables contain phenylalanine, which matters for people with phenylketonuria. People with aspirin-sensitive asthma should keep avoiding aspirin and NSAIDs such as ibuprofen.

Who should be careful

Talk to your doctor or pharmacist before starting montelukast if you or your child have a history of depression, anxiety, sleep problems or self-harm, or if it is being suggested for hay fever alone, where antihistamines or steroid nasal sprays are the usual first steps. Never stop or start it on your own when it is part of an asthma plan; a low score does not mean it is the wrong medicine for you.

How we scored it

Overdose marginOverdose marginHow far a normal dose is from a harmful one. A wide margin means an accidental extra dose is unlikely to cause serious harm.More in the glossary (95), dependence (95) and interactions (92) are excellent. Regulatory warnings (35) is the weakest factor, reflecting boxed warningsBoxed warningThe strongest safety warning the US FDA puts on a medicine's label, printed inside a black border at the top.More in the glossary in three countries and the second-line restriction for hay fever. Serious side effects (62) balance rare but grave psychiatric events against a large majority of users who have none.