Pros don't get sick (most of them anyway) because of two reasons:
1. They take every possible prevention drug in the world to protect themselves. I personally spend much more on accessories than I do on the gear itself.
2. Pros have the genetics to accept the gear. Most pros get healthier on the gear than off. Personally, all my blood tests ON the gear are absolutelly perfect and I feel great. Off the gear, my blood tests are screwed up and I feel like shit. That's the main 'pro secret' - the ability for the body to accept the gear, in any amount and not just not have any side effects, but actually to thrive on the gear.
Regarding the insulin - again, you won't become diabetic if you take all the necessary precautions.