Montelukast

Montelukast is an oral anti-inflammatory medicine of the class known as leukotriene receptor antagonists, sometimes called leukotriene-modifying agents. It specifically blocks the cysteinyl leukotriene receptor, interrupting a chemical signaling pathway that contributes to asthma and allergic disease ^[1].

The drug was approved by United States regulators in 1998 and marketed as Singulair; it became available as a generic after 2012 and is now one of the more commonly prescribed medicines in the United States ^[1]. It is taken by mouth and is formulated as standard tablets, chewable tablets and oral granules, the last making it convenient for young children ^[1].

Montelukast is used mainly for the long-term, maintenance control of asthma, although treatment guidelines generally place it below inhaled corticosteroids as a preventer; it does not relieve an asthma attack once one has begun. It is also used for allergic rhinitis (hay fever) and to prevent exercise-induced narrowing of the airways ^[1]. Following safety concerns, regulators have advised reserving montelukast for allergic rhinitis only when other treatments are inadequate or not tolerated ^[1].

The most prominent safety issue is neuropsychiatric. Reports of mood and behavior changes led the United States Food and Drug Administration to add a boxed warning in 2020, its strongest form of caution, listing effects such as nightmares, insomnia, depression, anxiety and agitation ^[1]. Systematic reviews of the evidence have reached mixed conclusions: several found no clear link with suicide or depression, while others detected possible associations with anxiety and sleep disturbances, particularly in certain age groups, and reviews in children likewise report predominantly gastrointestinal and neuropsychiatric adverse effects ^[2][3][4]. The overall risk remains difficult to quantify, and careful monitoring is advised ^[3].

Montelukast is a prescription medicine that is generally well tolerated, with headache and abdominal pain among the most common effects. Its most important concern is a range of neuropsychiatric effects, including mood changes, agitation, sleep disturbance, vivid dreams and rarely suicidal thoughts, which prompted a boxed warning. Rarely, reducing oral steroids while on it can unmask an eosinophilic condition affecting blood vessels. It should not be relied on for acute attacks.

Montelukast has fewer clinically important interactions than most respiratory drugs, and those that exist run largely in one direction: other drugs changing montelukast exposure rather than the reverse.

Montelukast is cleared mainly by CYP2C8, with CYP3A4 and CYP2C9 contributing. Gemfibrozil, a strong CYP2C8 inhibitor, raises montelukast AUC about 4.5-fold and triples its half-life, mostly because gemfibrozil's glucuronide metabolite blocks formation of the M6 metabolite. Strong enzyme inducers work the other way; phenobarbital cuts montelukast AUC by roughly 40%, and rifampin is expected to behave similarly. That shows up as loss of asthma control rather than as a side effect, which makes it easy to miss.

Montelukast is itself a potent CYP2C8 inhibitor in liver microsomes, but this has not translated into meaningful inhibition at ordinary doses in people.

Nothing in the interaction profile speaks to the neuropsychiatric adverse effects montelukast carries a boxed warning for; those appear independent of other medication.

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Montelukast was discovered and developed by Merck (Merck Frosst) in Canada during the 1990s as an orally active, once-daily antagonist of the cysteinyl leukotriene receptor. It arose from a broad effort to translate the newly understood biology of the leukotrienes, inflammatory mediators of asthma, into a convenient pill. It received US FDA approval in 1998 under the brand name Singulair for asthma, with allergic rhinitis indications following. As a well-tolerated tablet suitable for children and adults, it became one of the best-selling respiratory medicines of its era, and generic versions appeared after the patent expired around 2012. In 2020 the FDA added a boxed warning about the risk of serious neuropsychiatric events, a development that has since shaped prescribing.

Montelukast is widely valued for its convenience and gentleness on the airways; a single daily tablet that helps control asthma and calm allergic rhinitis without the technique demands of an inhaler or the concerns of oral steroids. It has been especially popular in children and in people whose asthma is closely tied to allergies or exercise, and a 2024 meta-analysis found that combining it with an antihistamine improved nasal symptoms more than antihistamine alone. Its once-daily oral dosing and long clinical track record are genuine strengths. In fairness, it is not a rescue medicine and does not open constricted airways during an attack, and the 2020 boxed warning about mood and behavior changes has appropriately made prescribers more cautious. For the right patient, monitored sensibly, it remains a useful and well-established controller.