If it was the ABC Australia news article that has been going around in FB that you saw, well, as mentioned in my other post, the news article stated 90 reports, not 90%.
There was a clinical review done by the American Academy of Pediatrics, but no clinical trials made. A clinical review means they reviewed all the adverse reactions attributed to montelukast/singulair and checked if there was indeed the drug that caused it or if there was something else. For an adverse reaction to be attributed to the drug, there should be a good temporal relationship kasi. A clinical trial, on the other hand, would require getting subjects/patients, giving them the drug and checking if they would exhibit the neuropsychiatric symptoms mentioned.
As a result of the clinical review, the US FDA did change the labeling of the side effects as early as 2009 and listed it under "rare" side effects as I mentioned in my earlier post. There is no attempt to hide this side effect from the public.
All medications, whether synthetic or herbal have side effects. As a side effect, it means that you cannot tell which patient would manifest with the side effects. Clinicians are advised to stop the medication if their patients manifest with the said side effects. That is why it is important to follow up with your doctors once treatment is initiated, not only to assess response to the medication but also to check for side effects or adverse reactions.
Clinicians also have to gauge need vs risk. For example, there are studies now linking the use of paracetamol in pregnancy to the same behavioral issues (aggression, hyperactivity, anxiety) in kids. So what do we do? Do we not give paracetamol to a febrile pregnant patient? What if the fever progresses and harms the pregnancy?
Another example, there were studies that linked folic acid use in pregnancy to development of asthma in kids. So again, are we going to stop giving folic acid to pregnant women because there is a possible risk of asthma? Folic acid deficiency in pregnancy is linked to neural tube defects and folic acid is therefore, vital, to a healthy pregnancy.
I fully agree that patient education is very important and all parents should really be aware of possible adverse reactions. But, with everything that is coming out in the internet nowadays, we should be more discerning of the articles that we read. Better to read from reputable websites like the cdc, us fda, acip, aap, etc. as well as to discuss these concerns with your primary care providers. Your doctors are there to educate and enlighten.