Singulair question

I'm trying to figure out what this Doctor means. Is he pointing out the growing body of evidence that Singulair causes other issues while on the medication, or that Singulair potentially causes these issues long-term even after stopping it?

My own Dr does not understand MCAS as they admitted, but they're trying to follow the protocol and prescribed Singulair along with the usual suspects. I'm in awful shape and we need to snap me out of this immediately but I said no to Singulair until an allergist can see me because of this Instagram content. I expect my local allergist will say the same thing as my own Dr and prescribe Singulair because they don't know about these Singular side effects.

Is there any alternative to Singulair? Singulair treats what, flushing and breathing, or is it more than that? My own doctor did not say how short the proposed Singulair course would be, or if it would be long. Do you know anything about these side effects?

https://www.instagram.com/reel/DDgAFhvRfmO/

Please forgive me if I am repeating known things, I am very new to this.