After about 4-6 weeks u should notice if your going to gain weight or not. I was on unbelievably high doses of inhaled steroids for 20 years and I never put on weight (this may be because I was put on theophylline too) but it also decreases muscle mass to a lesser extent. I did notice the latter a lot because I am very thin with no muscle mass! Corticosteroids can also cause insulin resistance which leads to accelerated ageing believe it or not!!! Its side effects are varied and many :(