Litigator’s Guide to Singulair Side Effects

Singular (montelukast sodium) is a prescription drug commonly used to treat allergies and asthma. It first received FDA approval in 1998. Singulair is manufactured by Merck. At the time of its release, the only adverse effect linked to Singulair was insomnia.

Singulair is categorized as a leukotriene receptor antagonist (LTRA). Leukotrienes are compounds in the lungs that accelerate the processes behind an asthma attack. Singulair works to actively block these compounds. The drug also reduces pro-inflammatory cells called neutrophils.

Singulair is intended to prevent asthma attacks and relieve common allergy symptoms. It is not a fast-acting medication and does not replace a rescue inhaler. Singulair is taken once daily and is available to individuals as young as 12 months. It’s available as granules, chewable tablets, and swallowable tablets.

After Singulair had been on the market for 10 years, the FDA began investigating reports of associated mood side effects. The Agency based its investigation on user data from its Adverse Event Reporting System (FAERS). The FDA ultimately added a warning about possible neuropsychiatric events while taking Singulair.

In the years following, research studies continued to examine the sudden onset of neuropsychiatric symptoms in Singulair users. From this body of research, suicidal ideation was more frequently reported in children. Other reported side effects include headache, insomnia, behavioral changes, and mood swings. Multiple studies also report that symptoms often resolve shortly after ceasing Singulair treatment.

After observing extensive adverse event reporting, the FDA reconsidered Singulair’s warning label. This change was also prompted by a letter from the Parents United for Pharmaceutical Safety and Accountability and the Montelukast (Singulair) Side Effects Support and Discussion Group. This letter implored the FDA to revise Singulair’s warning message. It argued the current label did not “adequately capture the scope and magnitude” of adverse effects.

The Agency was also influenced by a 2019 Pediatric Advisory Committee meeting detailed all known adverse effects of Singulair. Per the Committee, these side effects included, “agitation, aggressive behavior or hostility, anxiousness, depression, disorientation, disturbance in attention, dream abnormalities, dysphemia (stuttering), hallucinations, insomnia, irritability, memory impairment, obsessive-compulsive symptoms, restlessness, somnambulism, suicidal thinking and behavior (including suicide), tic, and tremor.”

In 2020, the FDA instated a black box warning on Singulair packaging. The message explains the drug carries a risk of “serious mental health side effects.”