Currently, there is not a boxed warning in the Product Information (PI) for montelukast medicines, including the originator brand, Singulair.

However, there is a known association between montelukast and neuropsychiatric events (such as agitation, sleep disturbance and depression) including, in rare cases, suicidal thinking and behaviour. These risks are well documented in both the PI and Consumer Medicine Information (CMI), which are the documents used by health professionals and consumers respectively to communicate safety information about a medicine.

In 2024, an updated safety investigation was conducted by the TGA after international regulators strengthened their warnings about neuropsychiatric events. The TGA investigation included seeking expert advice from the Advisory Committee on Medicine at their August 2024 meeting). The relevant ACM meeting statement is available on the TGA website.

The ACM advised that: the updated evidence did not identify any new neuropsychiatric risks, and the existing evidence for the association between montelukast and neuropsychiatric risks had not changed and remained uncertain.

However, on balance, the ACM advised that while the scientific and clinical evidence to 2024 does not demonstrate a causal association between montelukast and neuropsychiatric symptoms, alignment with international regulators in this case and in acknowledgment of consumer concerns, it would now be appropriate to implement a boxed warning. In formulating the boxed warning, the ACM supported careful wording that neuropsychiatric events are generally mild and may be coincidental.

The TGA is currently progressing the recommendations of the ACM to strengthen the information in the Australian PI.

And for context here is some info on who/what ACM are, as well:

https://www.tga.gov.au/about-tga/advisory-bodies-and-committees/advisory-committee-medicines-acm