I've been on inhaled asthma medication since I was 4. I started on Intal, then got switched to Becotide then Qvar (the watered down, environmentally friendly poor substitute) in my 20s.
For a start, don't confuse corticosteroids with anabolic steroids, asthma medication won't build muscle or shrink your bits. Corticosteroids do leave you more open to osteoporosis later in life so I'm informed. All they are is a glorified anti-inflammatory to open up airways.
Until I got a long term knee injury in january I'd been riding 52 weeks a year on a mountain bike for 7 years. I certainly lost weight, over a stone, and four inches from my waist, but have put some back in muscle mass. Apart from being able to breathe properly, I don't put anything down to the medication.