Ah, a fellow dipper. Honestly, it's a terrible habit and you should set a date to quit. I'm planning on quitting in mid-June after I graduate. But to your question, I can't say if it has any direct effect on muscle growth. I do know it speeds up your ****bolism and suppresses appetite, so for those who are already hard-gainers (a term I use loosely), it will certainly make things more difficult. If you're like me and you have a slower ****bolism though, it probably won't make much difference. Then again, I don't use very heavily at all, compared to the average.