Montelukast
Prescription status is set country by country — the label where you live is the one that applies.
Beta: the medication section is still being tested, and its data may contain errors. Do not rely on it for a decision about your own treatment.
Montelukast is a leukotriene receptor antagonist. It blocks the action of cysteinyl leukotrienes, inflammatory mediators that constrict the airways and drive swelling and mucus, so it damps the inflammatory side of asthma rather than relaxing muscle directly. It is taken as a tablet for asthma control and, where the label allows, for allergic rhinitis: in Finland, Fimea approves rhinitis relief only in people already taking the tablet for asthma. It is not a rescue treatment.
A usual adult range, not a national label — the dose and the timing differ by country and by product.
Approved uses differ by country — some of these may be off-label or unapproved where you live.
It works over days, so a reliever inhaler is still needed for sudden symptoms and the tablet is continued even when breathing feels fine. Food does not matter much, and it is usually taken in the evening, which fits the night-time and early-morning pattern of asthma symptoms. The reason for the mood warning is a recognised class effect on the nervous system: sleep disturbance, vivid dreams, irritability, anxiety, low mood and, rarely, thoughts of self-harm have been reported, in adults and children alike, sometimes soon after starting.
New or worsening low mood, agitation, unusual behaviour changes, or any thoughts of self-harm mean see a doctor without delay. Asthma that keeps worsening despite regular use, or rising reliever need, also needs review.
Reference information, not medical advice. Discuss any change with your doctor.