Montelukast/Singulair now has a "black box" warning by the FDA due to neuropsychiatric events

The U.S. Food and Drug Administration is requiring a boxed warning – the agency’s most prominent warning – for montelukast (sold under the brand name Singulair and in generic form) to strengthen an existing warning about the risk of neuropsychiatric events associated with the drug, which is used to treat asthma and allergic rhinitis (hay fever).

The boxed warning advises health care providers to avoid prescribing montelukast for patients with mild symptoms, particularly those with allergic rhinitis.

Neuropsychiatric events included agitation, depression, sleeping problems, and suicidal thoughts and actions.

The incidence of neuropsychiatric events associated with montelukast is unknown as of 2020, but some reports were serious. Many patients and health care professionals are not fully aware of these risks as per Sally Seymour, M.D., director of the Division of Pulmonary, Allergy and Rheumatology Products in the FDA’s Center for Drug Evaluation and Research.

The drug was first approved in 1998. The FDA determined the risks of montelukast may outweigh the benefits in some patients, particularly when the symptoms of the disease are mild and can be adequately treated with alternative therapies. For allergic rhinitis in particular, the FDA has determined that montelukast should be reserved for patients who have not responded adequately to other therapies — or who cannot tolerate these therapies.
 
Importantly, there are many other safe and effective medications to treat allergies with extensive history of use and safety, such that many products are available over the counter without a prescription. Immunotherapy ("allergy shots") is a safe treatment used for more than 120 years, widely available, prescribed and managed by board-certified allergists in the U.S.

In addition to the boxed warning, the FDA is also requiring a new Medication Guide to be given to patients with each montelukast prescription.

References:

https://www.fda.gov/news-events/press-announcements/fda-requires-stronger-warning-about-risk-neuropsychiatric-events-associated-asthma-and-allergy