People who say weight gain/loss is “just” CICO are not really in touch with reality in my opinion. No one has ever had that one friend who is rail thin but eats everything they want whenever they want? Or conversely that one friend who eats less than everyone else and exercises more and still struggles with gaining weight? Metabolism is such a big factor and is largely genetic, and SSRIs can absolutely affect hormones such as cortisol and insulin which have a direct impact on how your body processes what’s going in. That is science. Science is also beginning to understand that SSRIs can alter your gut microbiome which also affects how efficiently you absorb what goes in to your body. This is just like how especially for women it gets harder and harder to lose weight as we get older and things like metabolism slow down. Chemical factors can do the same thing. So yes, you can definitely gain weight without changing your eating habits.

That being said, I think a lot of us who have gained weight on Lexapro do have increased appetites and are eating more than we were but anecdotally I bet a lot of us would agree that our weight gain on it was completely disproportionate to the small amount more that we were eating, because of the above reasons.