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 substantially 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. Substantial state court litigation also proceeds in other jurisdictions including California, Pennsylvania, and Louisiana, alongside the New Jersey MCL.

The substantive 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 substantially 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 substantially 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 substantial preemption challenges, and the strategic considerations for affected patients pursuing claims.

What Singulair is and the alleged neuropsychiatric mechanism

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. The drug works by:

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

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).

Approved uses:

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:

Mood regulation
Impulse control
Sleep regulation
Anxiety response
Aggression response

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

Vulnerable populations. Studies suggest higher risk in:

Children (especially ages 2-18)
Adolescents
Elderly patients
Patients with existing mental health conditions

Documented adverse effects. The FDA boxed warning lists:

Suicidal thoughts and behavior
Depression
Aggression
Agitation
Sleep disturbances (insomnia, vivid nightmares)
Anxiety
Hallucinations
Restlessness
Disorientation
Behavioral changes

Duration of effects. Some plaintiffs allege psychiatric effects:

Begin during Singulair use
Persist after discontinuation (long-lasting neurochemical effects)
May contribute to permanent psychiatric injury in some cases

The alleged injuries

Plaintiffs in Singulair litigation allege various injuries:

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

Suicide attempts. Substantial suicide attempt cases:

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
Substantial medical expenses and lost wages from depression

Other psychiatric disorders. Various psychiatric conditions alleged:

Anxiety disorders
Panic disorders
Sleep disorders (long-term insomnia, recurring nightmares)
Aggression disorders
Hallucinations and psychotic episodes
Suicidal ideation without suicide attempt

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

Sudden onset of aggressive behavior
Personality changes
Behavioral regression
Academic decline
Social withdrawal
Self-injurious behavior

Vivid nightmares and sleep disorders. Frequently reported:

Recurring violent or disturbing nightmares
Sleep paralysis
Night terrors
Chronic insomnia
Daytime fatigue affecting work or school

The procedural history of Singulair litigation

The litigation has developed through several phases:

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 substantial 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
Substantial gap between actual risk and patient awareness

March 4, 2020. FDA mandates Singulair black box warning — the most serious FDA drug warning. The boxed 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. Merck retains liability for pre-spinoff conduct.

March 2022. New Jersey Multicounty Litigation (MCL) 637 established for Singulair cases in Middlesex County before Judge John C. Porto. Initial consolidation: 247 lawsuits.

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. Substantial Merck internal document production.

August 2024. Northern District of California grants Merck summary judgment in additional case based on similar preemption theory. California ruling addresses adult plaintiff cases.

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. FDA adverse event reports continue increasing.

Current status (May 2026). No federal MDL established. NJ MCL 637 active with substantial case inventory. Various state court litigation parallel to MCL. Mixed preemption rulings creating procedural uncertainty.

The federal preemption defense

The central legal issue in Singulair litigation is federal preemption:

FDA-approved warning defense. Merck argues that:

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

Plaintiff's response. Plaintiffs argue:

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

Mixed preemption rulings. Federal courts have split:

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

Adult vs. pediatric distinction. Some courts have:

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

Pre-2020 vs. post-2020 cases. Substantial distinction:

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 substantially changed the legal landscape

Generic montelukast. Additional complication:

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

Eligibility framework

The framework for filing Singulair claims:

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

Pharmacy records
Medical records showing prescription
Physician prescribing records
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
Mental health treatment records
Hospitalization records (if applicable)
Suicide attempt or completion documentation (if applicable)
Behavioral changes documented in school/work records (especially pediatric cases)

Causation evidence. Strong cases include:

Onset of psychiatric symptoms during Singulair use
No prior psychiatric history (or substantial 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

Strong case profile:

Pediatric patient (stronger pediatric warning failure case)
Pre-2020 injury (before boxed warning)
Documented neuropsychiatric injury
Clear temporal association with Singulair use
No prior psychiatric history
Substantial damages (medical expenses, lost wages, wrongful death)

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

Discovery rule typically applies
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 Singulair compares to other pharmaceutical mass torts

The litigation has distinctive features:

Compared to Zantac NDMA litigation: Both involve allegations against substantial pharmaceutical company. Zantac has substantial procedural issues (federal preemption ruling, MDL dismissal). Singulair has different preemption issues but better preserved cases in state courts.

Compared to Suboxone tooth decay litigation: Both involve neuropsychiatric medication producing alleged harms. Singulair has earlier and broader FDA action (2020 boxed warning); Suboxone litigation is more recently consolidated.

Compared to Tylenol autism litigation: Both involve common medication with alleged neurological/psychiatric effects. Tylenol litigation faces Daubert issues; Singulair faces preemption issues.

Compared to Ozempic litigation: Both involve consumer medications with serious side effects. Ozempic has broader physical injury allegations; Singulair focuses on neuropsychiatric.

Compared to Truvada/Tenofovir litigation: Both involve Merck (Singulair) and Gilead (Truvada) as major pharmaceutical defendants. Both use non-federal-MDL consolidation. Truvada uses informal federal coordination + CA JCCP; Singulair uses NJ MCL.

Distinctive Singulair features:

New Jersey Multicounty Litigation (state court consolidation), not federal MDL
Substantial preemption challenges
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)
Substantial Merck financial capacity for settlement

Settlement projections

Settlement valuation depends substantially on:

Resolution of preemption defense
Plaintiff age (pediatric stronger)
Injury severity
Timing of injury (pre-2020 stronger)
Documentation quality
Bellwether outcomes

Estimated settlement ranges (if cases proceed):

Pediatric suicide cases:

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

Adult suicide cases:

Substantial preemption challenges
If overcame preemption: $200,000 - $2,000,000+
Wrongful death valuation considerations

Severe non-fatal psychiatric injury:

Permanent psychiatric disability
Substantial medical expenses
Range: $100,000 - $1,500,000

Moderate psychiatric injury:

Documented but treatable conditions
Range: $25,000 - $500,000

Wrongful death (any age):

Parents/spouse/dependents claims
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 substantial settlements, particularly when other tax debt issues exist.

Strategic considerations

For affected patients and prospective plaintiffs:

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)

Document the psychiatric injury comprehensively. Critical evidence:

Mental health treatment records (therapy, psychiatry)
Hospitalization records (if applicable)
School records showing behavioral changes (pediatric)
Work records showing performance changes (adult)
Family observations (witness statements)
Death investigation records (for suicide cases)

Address the temporal association. Strong cases show:

Psychiatric symptoms began during or shortly after Singulair use
No substantial prior psychiatric history (or clear worsening)
Discontinuation produced any improvement
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).

Address the preemption issue strategically. Counsel should:

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. Their assessment of causation strengthens cases.

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 substantial settlements. Psychiatric injury settlements may have complex tax treatment. Coordinate with tax counsel for substantial settlements. Personal injury for physical injuries tax-free; emotional distress without physical injury may be taxable. Component allocation matters.

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 substantial procedural complications. The strongest cases involve pediatric patients with pre-2020 injuries, clear temporal association with Singulair use, no substantial prior psychiatric history, and substantial 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 substantial 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.