Rule of thumb is as long as you're below 1.5x upper limit of the normal IGF-1 range, you can probably stay there indefinately without developing acromegalic features. So this is for those planning on staying on forever. The higher you go beyond 1.5x, the less time there is before acromegalic changes occur. How long? No one can say for sure. I've read one example that showed a case where @ 2x IGF ULN noticeable changes took about 2 years.
And sorry, no, there are no studies intentionally injecting healthy bodybuilders with supra-physiologic doses until they develop the disease. We have to make our best guess from the available data. So far all we've seen are a handful of celebrities and athletes suspected of developing it, who'll never admit rHGH use. Until recently, running high doses daily for years was out of the question for anyone but the very wealthy.
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