Sure, other drugs like ibuprofen can lead to harmful problems in the body, so what? You can't "just listen to your body" with things like this. People with cancer feel fine for a while, often even to the point where they discover the lump, that doesn't mean that there isn't something wrong.
There will never be a precise cohort study in humans which is able to look at the precise dosages/cycles etc. All you can go by is examining the health outcomes in people such as these, and essentially theorizing from the level of competition they are at approximately what they used.
a 10 week cycle of anything might do absolutely nothing harmful, multiple 10 week cycles over 20 years certainly could.