RE: Is it possible to....
over what time scale are we talking no effect on the htpa? it will have some effect for a good few months i should imagine, but im sure it would return to normal after that. And im sure in the long term there would be no noticable side effects.
Gain alot of muscle and keep it? well, if your a good way below your genetic limit, and you have a sorted diet and manage to keep up the extra calories needed after the cycle then yes its possible to gain and keep some muscle, from experience 4-6 pounds kept lbm is about one cycle for a first timer, maybe a bit more. Some people post about gaining a stone or more but in my mind you cant gain that much lbm in 8 weeks.