@leslyb I'm sorry, my original comment was intended for the OP! I noticed my vision changed within the first few months of starting steroids. By the end of the second year I had to have both corneas replaced as my vision was 20-100, and I was no longer able to pass a driving test.

If you're on a high dose of steroids, adrenal suppression can begin as soon as after the first week, and that risk increases with prolonged use. Myopathy can begin at just 10mg of Prednisone a day for 4 weeks. At higher doses - in just 2-3 weeks. Long-term steroid use is considered 2-3 months. Everyone is different so what one person can tolerate may not be the same as someone else, but it doesn't really take very long for these unpleasant side effects to take effect.