Montelukast: important advice about mood, sleep and behaviour

Last Updated: Monday, 12 October 2026

Montelukast helps prevent asthma symptoms and is often taken alongside inhalers.

The MHRA, the UK medicines regulator, has strengthened warnings about changes in mood, sleep or behaviour. These side effects can affect adults, teenagers and children.

What should you watch for?

New or worsening symptoms include:

• Nightmares or difficulty sleeping.
• Anxiety, low mood or depression.
• Restlessness, irritability or aggressive behaviour.
• Problems with concentration or memory.
• Seeing or hearing things that are not there.
• Thoughts about self-harm or suicide.

What should you do?

Seek medical advice immediately if you or your child develops these symptoms. Your prescriber will advise about stopping montelukast and alternative treatment. If you cannot reach them, contact NHS 111.

Call 999 if someone has seriously harmed themselves or is at immediate risk of harm.

Tell family, friends or carers about this warning: they may notice changes you do not. Read the medicine leaflet.

Want to discuss your medicine?

Contact your GP practice to book a medication review with a clinician. Do not wait for a routine review if symptoms develop.

Read the full MHRA alert.