In March 2020, the FDA slapped its strongest possible warning — a Boxed Warning, commonly called a black box warning — on Singulair (montelukast), a drug that had been prescribed to millions of Americans for asthma and allergies since 1998. The warning came after years of mounting evidence linking the medication to serious neuropsychiatric side effects, including depression, anxiety, hallucinations, and suicide. The FDA had identified 82 completed suicides associated with montelukast use, with 19 of those cases involving patients aged 17 or younger. It took the agency more than two decades from the drug’s initial approval to require its most serious safety label — a delay that has left families, physicians, and state attorneys general asking why it took so long.
The story of Singulair’s mental health risks is not a simple one. The scientific evidence remains genuinely mixed, with some large-scale studies failing to find a statistically significant link between montelukast and depression or suicidal behavior, while individual adverse event reports and a 2025 meta-analysis tell a more troubling story. What is clear is that the drug was prescribed on an enormous scale — approximately 9.3 million patients received a dispensed prescription in 2018 alone — and that the FDA now says it should be reserved as a last resort for hay fever patients who have failed other treatments. This article examines the full timeline of the FDA’s warnings, what the science actually shows, who is most at risk, and what the ongoing litigation against Merck means for patients and families.
Table of Contents
- Why Did the FDA Take 22 Years to Add a Mental Health Warning to Singulair?
- What Mental Health Side Effects Has Montelukast Been Linked To?
- What Does the Science Actually Say About Singulair and Suicide Risk?
- What Should Patients Taking Singulair Do Now?
- The Lawsuits Against Merck and What They Allege
- Pediatric Patients and Disproportionate Risk
- Where the Singulair Story Goes From Here
- Conclusion
- Frequently Asked Questions
Why Did the FDA Take 22 Years to Add a Mental Health Warning to Singulair?
The FDA approved montelukast in February 1998 as a leukotriene receptor antagonist for asthma. It works by blocking chemicals in the body that cause airway inflammation, and it quickly became a blockbuster drug for Merck. For the first full decade it was on the market, there was no formal FDA communication about psychiatric risks. It was not until 2008 — ten years after approval — that the agency issued its first public notice about a pending investigation into possible links between montelukast and behavior or mood changes, suicidality, and suicide. That initial communication was far from a warning. It was an acknowledgment that the agency was looking into the problem. What happened next was telling. After the 2008 communication, adverse event reports spiked 18-fold, jumping from 41 reports in 2007 to 752 in 2008.
this pattern is well-documented in pharmacovigilance — once a possible side effect is publicly identified, patients and clinicians who had been attributing symptoms to other causes begin connecting them to the drug. The surge in reports did not necessarily mean the drug was suddenly causing more harm. It more likely meant that harm had been occurring undetected for years. Another 12 years passed before the FDA escalated to a Boxed Warning in March 2020, also requiring a medication Guide to be distributed with every prescription. By that point, the agency had accumulated enough case data, including 82 reported suicides, to conclude that the mental health risks warranted the most serious label it could mandate short of pulling the drug from the market. The delay has drawn sharp criticism. New York Attorney General Letitia James sent a letter to the FDA calling for immediate action, noting that tragic adverse events — including aggression, depression, and suicide — continued to be widely reported and were disproportionately affecting pediatric patients. For a drug given routinely to children for seasonal allergies, the stakes of a 22-year warning gap are hard to overstate.
What Mental Health Side Effects Has Montelukast Been Linked To?
The range of reported psychiatric side effects associated with Singulair is broad and, in some cases, severe. According to the FDA’s safety communication, reported symptoms include bad or vivid dreams, depression, disorientation and confusion, anxiety, hallucinations, irritability, restlessness, stuttering, and uncontrolled muscle movements. These are not the kinds of side effects most patients expect from an allergy pill or asthma maintenance medication. For parents who gave their children Singulair to manage mild seasonal allergies, reports of hallucinations or sudden personality changes were alarming. The FDA’s review of post-marketing data identified 82 completed suicides associated with montelukast use. Of those, 45 involved patients older than 17, 19 involved patients 17 and younger, and 18 cases had no age provided.
A critical caveat here: 48 of the 82 cases lacked sufficient information to fully evaluate whether the drug played a causal role. This is a genuine limitation of post-marketing surveillance data — adverse event reports establish association, not causation, and many cases come with incomplete medical histories. However, the sheer number of suicide reports linked to a single respiratory medication was unusual enough to warrant the FDA’s strongest warning. One aspect that makes montelukast’s psychiatric profile particularly concerning is that symptoms have been reported in patients both with and without pre-existing psychiatric conditions. This means a patient with no history of depression or anxiety could potentially develop these symptoms after starting the drug. Even more troubling, the FDA noted that in some cases, symptoms persisted after the medication was discontinued. This challenges the assumption that simply stopping the drug will resolve any psychiatric effects, and it raises difficult questions for patients who took montelukast for extended periods.
What Does the Science Actually Say About Singulair and Suicide Risk?
The scientific evidence on montelukast and mental health is genuinely mixed, and that ambiguity has made this issue particularly difficult for regulators, physicians, and patients. A 2025 meta-analysis published in Frontiers in Pharmacology found that montelukast was associated with an 11 percent higher risk of anxiety (a relative risk of 1.11), but it did not find a statistically significant increased risk of depression, suicidal behavior, or completed suicides. That finding cuts both ways — it validates the anxiety concerns but does not support some of the most serious allegations in the same way post-marketing reports do. An FDA-supported observational study through the Sentinel system — one of the largest safety surveillance networks in the country — examined 457,377 patients and found no association between montelukast and hospitalizations for depression or self-harm when compared to patients using inhaled corticosteroids. A separate pediatric study of 74,291 children found a non-significant hazard ratio of 1.31 for suicide or suicidal actions when comparing montelukast users to those on long-acting beta agonists.
Non-significant means the result could have occurred by chance, but a hazard ratio of 1.31 is not trivially small either — it suggests a possible 31 percent higher risk that the study was not large enough to confirm. Global pharmacovigilance data adds another layer. Fatal suicide rates among psychiatric adverse events reported with montelukast varied significantly by country: 0.17 percent in the United Kingdom, 1.88 percent in the United States, and 2.57 percent in the European Union. These differences likely reflect variations in reporting systems, prescribing patterns, and population characteristics rather than true differences in drug effects. The bottom line for patients and families is uncomfortable: the large controlled studies have not confirmed a causal link to suicide, but the volume of individual case reports and the biological plausibility of the mechanism were enough for the FDA to act. When a drug affects neurological pathways, rare but catastrophic outcomes can be real even if they do not show up reliably in population-level studies.
What Should Patients Taking Singulair Do Now?
The FDA’s 2020 Boxed Warning came with specific guidance that changed how montelukast should be prescribed. For allergic rhinitis — hay fever — the FDA now says montelukast should be reserved only for patients who cannot tolerate or do not respond to other allergy medications. This is a significant restriction. Before the warning, many physicians prescribed Singulair as a first-line or early option for seasonal allergies, particularly in children, because it was a once-daily pill with what seemed like a mild side effect profile. That calculus has shifted. Antihistamines, nasal corticosteroid sprays, and other allergy treatments should now be tried first. For asthma, the equation is different.
Montelukast remains an option, but physicians are now required to weigh the mental health risks against the respiratory benefits before prescribing. For some asthma patients, particularly those with exercise-induced bronchoconstriction or aspirin-sensitive asthma, montelukast offers genuine clinical benefit that may not be easily replaced. The tradeoff is more justifiable when the alternative is poorly controlled asthma, which carries its own serious health risks. But for a child with mild intermittent asthma who could be managed with an inhaler alone, the risk-benefit calculation looks very different than it did before 2020. Patients currently taking montelukast should not stop the medication abruptly without consulting their prescriber. What they should do is have a direct conversation about whether the drug is still necessary, whether alternatives exist for their specific condition, and what psychiatric symptoms to monitor. Given that symptoms have occurred in patients without prior psychiatric history and have in some cases persisted after discontinuation, ongoing awareness is important even after stopping the drug.
The Lawsuits Against Merck and What They Allege
The growing body of adverse event reports and the FDA’s belated Boxed Warning have fueled litigation against Merck, the pharmaceutical company that manufactures Singulair. Lawsuits accuse Merck of designing a defective drug, negligence, and failure to adequately warn patients and physicians about psychiatric risks. As of March 2022, 247 lawsuits were consolidated into multicounty litigation — designated MCL 637 — in New Jersey state court. No federal multidistrict litigation (MDL) consolidation had occurred as of January 2026, meaning the cases remain in state-level proceedings. Studies cited in the lawsuits allege that prolonged Singulair users are twice as likely to develop mental health disorders compared to non-users. Plaintiffs include families of children who experienced severe behavioral changes, adults who developed depression or anxiety while on the drug, and in some cases, families of individuals who died by suicide.
The core legal theory is that Merck knew or should have known about the psychiatric risks earlier and failed to provide adequate warnings to patients and the medical community. The 22-year gap between initial FDA approval and the Boxed Warning is central to this argument — plaintiffs contend that stronger warnings earlier could have prevented harm by prompting physicians to prescribe alternatives or monitor patients more closely. It is worth noting a limitation of these cases. The mixed scientific evidence described earlier means that establishing causation in individual cases will be challenging. Merck can point to the large observational studies that did not find statistically significant links to suicide or depression. Plaintiffs will counter with the FDA’s own decision to impose its strongest warning and the volume of adverse event reports. How courts weigh these competing narratives will likely shape the outcome of the litigation.
Pediatric Patients and Disproportionate Risk
The concern about Singulair’s psychiatric effects is sharpest when it comes to children. Montelukast has been widely prescribed to pediatric patients for both asthma and allergic rhinitis, and children may be less able to recognize or articulate psychiatric symptoms like confusion, anxiety, or changes in mood. A child experiencing vivid nightmares or sudden irritability may not connect those experiences to a medication, and parents may attribute behavioral changes to developmental phases, school stress, or other factors before considering a pharmaceutical cause.
New York Attorney General Letitia James specifically flagged the disproportionate impact on pediatric patients in her letter to the FDA. Of the 82 completed suicides the FDA identified, 19 involved patients aged 17 or younger — a deeply disturbing figure for a drug commonly given to school-age children for hay fever. The 18-fold spike in adverse event reports after the 2008 FDA communication suggests that many families only made the connection between their child’s behavioral changes and Singulair after learning that such a connection was possible. For parents of children currently taking montelukast, the FDA’s current position is clear: if the drug is being used for allergies and other treatments have not been tried, it is time to discuss alternatives with the child’s physician.
Where the Singulair Story Goes From Here
The Singulair saga is far from over. The New Jersey multicounty litigation is still proceeding, and its outcomes could set precedents for pharmaceutical failure-to-warn cases involving psychiatric side effects. Merck faces the challenge of defending a drug that the FDA itself determined warranted its most severe warning — a fact that will be difficult to neutralize in front of juries, regardless of what the population-level studies show. Meanwhile, montelukast remains on the market and continues to be prescribed, albeit with more caution and tighter guidelines than before.
The broader lesson from Singulair extends beyond a single drug. It raises fundamental questions about how long it should take for post-marketing safety signals to translate into meaningful label changes, and whether the current pharmacovigilance system moves fast enough to protect patients — especially children — from rare but devastating side effects. For families affected by Singulair’s psychiatric effects, the FDA’s 2020 Boxed Warning was overdue validation. For the millions of patients who took the drug without incident, it is a reminder that no medication is without risk, and that the absence of a warning label does not always mean the absence of danger.
Conclusion
Singulair’s journey from routine allergy and asthma medication to a drug carrying the FDA’s most serious warning label is a case study in how pharmaceutical safety signals can take decades to translate into meaningful patient protections. The FDA identified 82 completed suicides, received thousands of adverse event reports describing depression, anxiety, hallucinations, and behavioral changes, and ultimately concluded in 2020 that montelukast required a Boxed Warning and should no longer be used as a first-line allergy treatment. The 22-year gap between the drug’s approval and that warning remains difficult to justify, particularly given that approximately 9.3 million patients were filling prescriptions annually. For patients and families, the practical takeaway is straightforward.
If you or your child is taking montelukast for allergic rhinitis, talk to your doctor about whether other treatments should be tried instead. If the medication is being used for asthma, have an honest conversation about the risk-benefit balance for your specific situation. Monitor for psychiatric symptoms — including in patients with no prior mental health history — and report any changes promptly. The science on montelukast and mental health remains mixed at the population level, but the individual reports are serious enough that the FDA acted, and patients deserve to make informed decisions with that context in hand.
Frequently Asked Questions
Is Singulair still available by prescription?
Yes. The FDA did not pull montelukast from the market. It remains available but now carries a Boxed Warning about neuropsychiatric side effects, and the FDA recommends it be reserved as a last-resort option for allergic rhinitis.
Can Singulair cause mental health problems in people with no psychiatric history?
Yes. The FDA has noted that neuropsychiatric symptoms have been reported in patients both with and without pre-existing psychiatric conditions. Having no history of mental health issues does not eliminate the risk.
Do the mental health side effects go away after stopping Singulair?
In many cases, symptoms improve after discontinuation, but the FDA has documented cases where psychiatric symptoms persisted even after the medication was stopped. Patients should consult their physician before discontinuing and should continue monitoring for symptoms afterward.
How strong is the scientific evidence linking Singulair to suicide?
The evidence is mixed. The FDA identified 82 completed suicides in post-marketing reports, but large observational studies, including an FDA-supported Sentinel study of over 457,000 patients, did not find a statistically significant association between montelukast and hospitalizations for depression or self-harm. A 2025 meta-analysis found an 11 percent increased risk of anxiety but not of depression or suicidal behavior.
Are children at greater risk from Singulair’s side effects?
Children may be disproportionately affected because they are less likely to recognize or report psychiatric symptoms. The New York Attorney General specifically flagged the impact on pediatric patients, and 19 of the 82 reported suicides involved patients aged 17 or younger.
Is there a lawsuit I can join if Singulair harmed me or my family?
As of early 2026, 247 lawsuits against Merck have been consolidated into multicounty litigation (MCL 637) in New Jersey. Individuals who believe they were harmed by Singulair should consult an attorney experienced in pharmaceutical litigation to discuss their specific circumstances.
