Singulair (montelukast) neuropsychiatric lawsuit: how the litigation works and why the preemption defense matters

The Singulair (montelukast) neuropsychiatric lawsuit represents an active pharmaceutical litigation that took a different procedural path than most active mass torts. Rather than consolidation into a federal Multidistrict Litigation, cases were centralized in New Jersey Multicounty Litigation (MCL) 637, which began in March 2022 with 247 initial lawsuits before Judge John C. Porto in Middlesex County, New Jersey. The defendants are Merck & Co. Inc. (which manufactured Singulair through approximately 2021) and Organon & Co., the Merck spinoff that now markets the drug. state court litigation also proceeds in other jurisdictions including California, Pennsylvania, and Louisiana, alongside the New Jersey MCL.

The theory centers on neuropsychiatric injuries (depression, suicidal thoughts and behavior, suicide, aggression, hallucinations, anxiety, sleep disturbances, and other psychiatric events) allegedly caused by montelukast's ability to cross the blood-brain barrier and bind with brain receptors associated with mood and impulse control. The drug, originally approved by FDA in 1998 for asthma and seasonal allergic rhinitis, was prescribed to approximately 9 million U.S. patients annually before the FDA's March 2020 boxed warning fundamentally altered the medical community's view of the drug's risk profile. The FDA's investigation prior to the 2020 boxed warning had documented at least 82 suicides connected to montelukast, 31 of which involved patients 19 years of age or younger.

The procedural posture is complicated by federal preemption defenses based on Merck's argument that it could not unilaterally change the FDA-approved drug label. Several courts have accepted this preemption argument and granted summary judgment for Merck, including December 2022 in the Eastern District of Wisconsin and August 2024 in the Northern District of California. The Wisconsin decision dismissed a mother's lawsuit alleging that Singulair caused her son's suicidal and homicidal thoughts. The California ruling addressed cases involving adult plaintiffs and held that Singulair's existing warnings were not inadequate for physicians prescribing montelukast to adults. The preemption defense has affected which plaintiff profiles have the strongest case theories.

This is how the Singulair neuropsychiatric litigation actually works, the science behind the alleged neuropsychiatric mechanism, the procedural history through the boxed warning and consolidated litigation, the eligibility framework for current and prospective plaintiffs, the preemption challenges, and the strategic considerations for affected patients pursuing claims.

What is Singulair and how does it allegedly cause neuropsychiatric effects?

Singulair (montelukast) is a leukotriene receptor antagonist approved for asthma and allergic rhinitis. The alleged neuropsychiatric mechanism involves montelukast crossing the blood-brain barrier and binding to brain receptors associated with mood regulation, impulse control, and sleep. This binding can allegedly cause depression, suicidal behavior, aggression, hallucinations, and other psychiatric effects documented in the FDA's 2020 boxed warning.

Singulair (generic name montelukast) is a selective leukotriene receptor antagonist, a class of drugs that block leukotrienes, chemical substances in the body that cause inflammation, swelling, and constriction in the airways.

Blocking leukotrienes. Leukotrienes (specifically LTD4 and LTE4) bind to receptors in airways and other tissues, causing inflammation.

Reducing airway inflammation. With leukotrienes blocked, airway inflammation decreases, helping with asthma symptoms.

Allergic rhinitis relief. The same mechanism helps with seasonal and perennial allergic rhinitis (hay fever) symptoms.

Once-daily oral dosing. Unlike inhaled asthma medications, Singulair is taken as a daily pill (tablet, chewable tablet, or oral granules).

• Prevention and chronic treatment of asthma in patients age 12 months and older
• Relief of seasonal allergic rhinitis in patients age 2 years and older
• Relief of perennial allergic rhinitis in patients age 6 months and older
• Prevention of exercise-induced bronchoconstriction

The neuropsychiatric mechanism. The current scientific understanding of how Singulair allegedly causes neuropsychiatric effects:

Blood-brain barrier penetration. FDA-conducted research on rats showed montelukast penetrates the brain, substantially more than the drug's original label "minimal distribution in the brain" claim suggested.

Brain receptor binding. FDA studies demonstrated montelukast binds with multiple brain receptors, particularly those associated with psychiatric effects including:

Specific receptor targets. Research has identified montelukast interactions with:

• BLT1 and BLT2 leukotriene receptors in the brain

• Receptors associated with mood regulation

• Receptors implicated in suicidal ideation

• Children (especially ages 2-18)

• Patients with existing mental health conditions

Documented adverse effects. The FDA boxed warning lists:

Duration of effects. Some plaintiffs allege psychiatric effects:

• Persist after discontinuation (long-lasting neurochemical effects)
• May contribute to permanent psychiatric injury in some cases

What injuries are alleged in Singulair lawsuits?

Plaintiffs allege injuries ranging from suicide and suicide attempts to severe depression, anxiety disorders, hallucinations, aggression, and behavioral changes in children. The FDA documented at least 82 suicides connected to montelukast before the 2020 boxed warning, with 31 involving patients age 19 or younger. Many cases involve patients with no prior psychiatric history.

Suicide. The most severe outcome, alleged in numerous wrongful death cases:

• Documented by FDA review prior to boxed warning

• 31 of 82 FDA-documented suicides involved patients 19 or younger

• Often involved patients with no prior suicide ideation

• Wrongful death claims pursued by surviving family members

• Patients with documented attempts during or after Singulair use

• Patients with documented post-Singulair psychiatric hospitalization

• Patients with permanent injuries from suicide attempts

Severe depression. Major depressive disorder allegedly caused or exacerbated by Singulair:

• New onset depression in patients without prior history

• Worsening depression in patients with mild prior history

• Treatment-resistant depression following Singulair use

• Medical expenses and lost wages from depression

• Sleep disorders (long-term insomnia, recurring nightmares)

• Suicidal ideation without suicide attempt

Behavioral changes in children. Particularly disturbing pattern in pediatric cases:

• Recurring violent or disturbing nightmares
• Daytime fatigue affecting work or school

What is the timeline of Singulair neuropsychiatric litigation?

Singulair litigation traces from the drug's 1998 commercial launch through the FDA's March 2020 boxed warning, the first lawsuits in August 2020, and the establishment of New Jersey MCL 637 in March 2022. Federal courts have issued mixed rulings on Merck's preemption defense. No federal MDL has been established, and bellwether case selection continues as of 2026.

1996. FDA initially approves montelukast (Singulair) for asthma treatment.

1998. Merck launches Singulair commercially in the U.S. market.

2007. Initial reports of association between montelukast and neuropsychiatric events begin appearing in medical literature.

2008. Merck updates Singulair warning label with "Precautions" section addressing post-marketing reports of agitation, aggression, anxiousness, dream abnormalities, and other neuropsychiatric events.

August 28, 2009. FDA announces update to Singulair's "Precautions" section requiring more neuropsychiatric warnings, including postmarket cases of agitation, aggression, anxiousness, dream abnormalities, depression, hallucinations, insomnia, suicidal thinking and behavior.

2018-2019. FDA reviewer Mariam Eljanne completes assessment of montelukast adverse events documenting:

• Thousands of neuropsychiatric event reports
• 82 suicides connected to montelukast
• 31 suicides in patients 19 or younger
• Gap between actual risk and patient awareness

March 4, 2020. FDA mandates Singulair black box warning, the most serious FDA drug warning.

• Lists suicide, depression, aggression, suicidal thoughts as serious risks
• Recommends montelukast not be used for mild allergic rhinitis (alternatives available)
• Restricts indications and recommends careful use
• Requires Medication Guide with each prescription

August 2020. First wave of Singulair lawsuits filed in various jurisdictions.

2021. Merck spins off Organon as separate publicly traded company. Organon assumes responsibility for Singulair marketing going forward.

March 2022. New Jersey Multicounty Litigation (MCL) 637 established for Singulair cases in Middlesex County before Judge John C. Porto.

December 2022. Eastern District of Wisconsin grants summary judgment for Merck in case involving mother's lawsuit over son's suicidal and homicidal thoughts. Ruling based on federal preemption: Merck couldn't unilaterally change the drug label.

2023-2024. Active discovery and motion practice in NJ MCL 637 and parallel state court litigation.

August 2024. Northern District of California grants Merck summary judgment in additional case based on similar preemption theory.

Late 2024-2025. JPML repeatedly declines to consolidate Singulair cases into federal MDL. Cases continue in state courts and NJ MCL 637.

2025-2026. Active mediation activity, bellwether case selection in NJ MCL 637, continued state court proceedings.

Current status (May 2026). No federal MDL established. NJ MCL 637 active with substantial case inventory.

How does the federal preemption defense work in Singulair cases?

Merck argues that federal law preempts state failure-to-warn claims because it could not unilaterally change the FDA-approved Singulair label. Under the Supreme Court's Wyeth v. Levine framework, preemption applies only when "clear evidence" shows the FDA would have rejected a stronger warning. Federal courts have split on this issue, with outcomes often depending on plaintiff age, injury timing, and whether brand or generic montelukast was used.

The central legal issue in Singulair litigation is federal preemption:

• FDA approved the Singulair label including warnings
• Manufacturer cannot unilaterally change FDA-approved label
• State law claims requiring different warnings are preempted by federal law
• Wyeth v. Levine, 555 U.S. 555 (2009) provides framework

Wyeth v. Levine framework. Supreme Court decision establishing:

• State law failure-to-warn claims are NOT automatically preempted

• Manufacturer can use "Changes Being Effected" (CBE) regulation to update labels

• Preemption applies only when manufacturer shows "clear evidence" FDA would not have approved stronger warning

• Plaintiff burden is to identify newly acquired information triggering CBE update obligation

• New scientific evidence emerged about neuropsychiatric risks

• Merck should have used CBE process to strengthen warnings

• Merck had access to internal data showing higher risk than label suggested

• "Newly acquired information" standard satisfied by post-marketing reports

• Some courts grant summary judgment for Merck (preemption applies)

• Other courts deny summary judgment (preemption doesn't apply on this record)

• Outcome often depends on specific plaintiff facts and timing of injury

• Found preemption applies to adult plaintiff cases (existing warnings adequate for adults)

• Permitted pediatric cases to proceed (different warning standards for children)

• Distinguished cases based on warning timing relative to injury date

• Cases involving injuries BEFORE March 2020 boxed warning have stronger failure-to-warn theory

• Cases involving injuries AFTER March 2020 boxed warning face stronger preemption defense

• The 2020 boxed warning changed the legal landscape

• Generic manufacturers face different preemption rules under PLIVA v. Mensing, 564 U.S. 604 (2011)

• Generic manufacturers' preemption defense substantially stronger

• Plaintiffs taking generic montelukast face procedural complications

Who is eligible to file a Singulair lawsuit?

Eligible plaintiffs include anyone who took brand-name Singulair or generic montelukast and developed documented neuropsychiatric injuries during or after use. The strongest candidates are pediatric patients with pre-2020 injuries, no prior psychiatric history, clear temporal association between drug use and symptom onset, and documented damages such as hospitalization records or wrongful death claims.

Singulair (or generic montelukast) use. Documented prescription or use:

• Sufficient time of use (typically 30+ days for psychiatric effects)
• Both brand-name Singulair and generic montelukast use can support claims (with generic manufacturer complications)

Neuropsychiatric injury during or after use. Documented psychiatric injury:

• Clinical diagnosis of psychiatric condition

• Suicide attempt or completion documentation (if applicable)

• Behavioral changes documented in school/work records (especially pediatric cases)

• Onset of psychiatric symptoms during Singulair use

• No prior psychiatric history (or worsening of prior history)

• Discontinuation produced improvement (in some cases)

• Re-challenge with Singulair produced recurrence (rare but compelling)

• Healthcare provider documentation of suspected Singulair association

• Pediatric patient (stronger pediatric warning failure case)

• Pre-2020 injury (before boxed warning)

• Clear temporal association with Singulair use

• Damages (medical expenses, lost wages, wrongful death)

Statute of limitations analysis. Most states have 2-4 year limitations:

• Some plaintiffs may benefit from delayed discovery (didn't know cause until later)
• 2020 boxed warning may toll limitations for some plaintiffs (notice of connection)

How does the Singulair lawsuit compare to other pharmaceutical mass torts?

Singulair litigation is distinctive because it was centralized in New Jersey state Multicounty Litigation rather than a federal MDL. It faces unique federal preemption challenges, benefits from the FDA's 2020 boxed warning establishing acknowledged neuropsychiatric risk, and draws important legal distinctions between pediatric and adult plaintiffs and between pre-2020 and post-2020 injuries.

• New Jersey Multicounty Litigation (state court consolidation), not federal MDL
• FDA boxed warning establishing acknowledged risk
• Mixed federal court rulings creating procedural uncertainty
• Pediatric cases distinguished from adult cases
• Pre-2020 cases stronger than post-2020 cases
• Both brand and generic manufacturers as potential defendants (with different preemption analysis)
• Merck financial capacity for settlement

What are the projected Singulair lawsuit settlement amounts?

Pediatric suicide cases carry the highest potential range of $500,000 to $5,000,000 or more. Severe non-fatal psychiatric injuries may range from $100,000 to $1,500,000. Adult cases face stronger preemption challenges that may reduce valuations.

• Strongest case theory (pediatric patient + serious injury + clear neuropsychiatric mechanism)

• Range: $500,000 - $5,000,000+

• Wrongful death cases (parents' loss) can be substantially higher

• Add wrongful death valuation framework

• Range varies substantially by state

Tax implications. Personal injury settlements for physical injuries are tax-free under IRC §104(a)(2). Psychiatric injury cases may have more complex tax treatment: emotional distress not arising from physical injury may be taxable. Coordinate with tax counsel for settlements, particularly when other tax debt issues exist.

What strategic considerations matter for Singulair plaintiffs?

Plaintiffs should thoroughly document their prescription history and psychiatric injuries, establish clear temporal association between Singulair use and symptom onset, and engage mass tort counsel experienced with NJ MCL 637 procedures and preemption defense issues. Pediatric patients with pre-2020 injuries, no prior psychiatric history, and well-documented damages have the strongest case profiles.

Document the prescription history thoroughly. Strong cases include:

• Pharmacy records showing Singulair prescriptions and refills

• Medical records showing prescribing physician

• Insurance records showing covered prescriptions

• Pre-2020 prescriptions especially valuable

• Generic montelukast prescriptions also relevant (with complications)

• Mental health treatment records (therapy, psychiatry)

• School records showing behavioral changes (pediatric)

• Work records showing performance changes (adult)

• Death investigation records (for suicide cases)

• Psychiatric symptoms began during or shortly after Singulair use

• No prior psychiatric history (or clear worsening)

• Clear temporal pattern between drug exposure and symptom onset

Engage experienced mass tort counsel familiar with NJ MCL 637. New Jersey MCL practice has specific procedural requirements. Counsel familiar with both NJ MCL and state court parallel litigation handles these cases more effectively. Most firms work on contingency basis (typically 30-40% of recovery).

• Identify when the injury occurred (pre-2020 stronger)
• Identify plaintiff age (pediatric stronger)
• Identify whether brand or generic montelukast was used
• Consider state court vs. NJ MCL strategy

Plan for extended timeline. With mixed preemption rulings and ongoing consolidation:

• Case resolution likely 2026-2029
• Bellwether outcomes will substantially affect settlement framework
• Some plaintiffs may benefit from waiting for procedural developments
• Statute of limitations protection essential

Address criminal/wrongful death framework. For suicide cases:

• Estate has standing for wrongful death claim
• Surviving family members may have separate claims
• State wrongful death statute determines specific framework
• Procedural complications with criminal investigation (if applicable)

Watch for related medication exposure. Many patients had:

• Multiple psychiatric medications during relevant period
• Other potential causes of psychiatric injury
• Coordinated medical evaluation needed for causation analysis
• Defense will emphasize alternative causation

Coordinate with treating providers. Treating psychiatrists, family physicians, and other healthcare providers are important witnesses.

Address the generic montelukast issue carefully. If patient took generic:

• Generic manufacturer preemption defense is substantially stronger (PLIVA v. Mensing)
• Brand-name manufacturer (Merck) liability may still apply under "innovator liability" theory in some states
• Specific state law determines viability of generic-only cases
• Some states permit cases against brand manufacturer even for generic-only patients

Plan for the procedural uncertainty. Mixed preemption rulings mean:

• Outcome depends on specific case facts
• Bellwether outcomes will provide clarity
• Settlement framework will emerge from procedural developments
• Patience and strong documentation are essential

Consider state court vs. NJ MCL filing. Specific advantages to:

• NJ MCL 637: Consolidated procedures, established framework, judicial expertise
• State court (California, Pennsylvania, etc.): Different procedural law, jury characteristics, potentially better outcomes
• Counsel should evaluate based on specific case facts

Address tax planning for settlements. Psychiatric injury settlements may have complex tax treatment. Personal injury for physical injuries tax-free; emotional distress without physical injury may be taxable.

Document the lack of warning. Critical evidence includes:

• Prescribing physician didn't know about neuropsychiatric risks
• Patient/parent didn't know about neuropsychiatric risks
• Prescription was for mild condition (would warrant safer alternative)
• Black box warning would have changed prescribing decision

For affected patients with documented Singulair-related psychiatric injury, the litigation provides paths to compensation despite procedural The strongest cases involve pediatric patients with pre-2020 injuries, clear temporal association with Singulair use, no prior psychiatric history, and documented damages. The work for plaintiffs is in comprehensive documentation including prescription records and psychiatric treatment records, engagement with experienced counsel familiar with NJ MCL practice and the preemption issues, careful coordination of state court vs. MCL strategy based on specific case facts, and informed monitoring of bellwether and preemption ruling developments. The FDA's 2020 black box warning fundamentally established that the neuropsychiatric risks were substantial and previously under-warned, but the legal framework for compensating pre-warning injuries continues developing through ongoing litigation. For plaintiffs with strong documented pediatric cases and clear neuropsychiatric injuries, the eventual resolution should produce meaningful compensation reflecting the serious nature of psychiatric injuries allegedly caused by inadequately warned medication used widely in pediatric populations.