Medical question: inability to access medication

In my work in progress (set in future based on our world, 20 years later), I have a character with muscular dystrophy. He's in his late teens and is ambulatory thanks to the muscle replacement technology but he is dependent on anti-rejection and steroids to help maintain cardiac and respiratory strength. (Steroids are part of current treatment for DMD to help boys maintain some muscle strength.)

Early on in the story, he will no longer be able to get his medications. I was wondering if anyone can give me an educated guess on how long it would be before this would begin to effect him physically? Weeks? Months?

TIA

Yikes, I hadn't even considered the possibilities of medication withdrawal, just the longer term health implications! Definitely have to look that up. This helps a lot!