Does smoking effect the muscle building process? I understand it can effect your endurance.
In my experience, the most detrimental aspect of smoking while bodybuilding is the lack of energy.
When I smoked, I was quite lethargic most of the time and in gym I used to just quit whenever it got too hard, or took too much energy.
Since I didn't feel fresh or rejuvinated even after a good nights sleep, going to the gym was usually out of the question, because I just didn't feel like it.
From a medical standpoint, probably the most detrimental aspect of smoking is lack of oxygen. Whilst smoking, the oxygen intake is lessened and it is replaced by various other elements, usually, ones bad for the body.
Also, the toxins that the cigarettes contain may lead to various diseases, in which case, doing serious weight training is probably out of the question.
Standard Disclaimer: I am not a doctor, so anything I say should not be considered an advice to bet your health on.
Not to direct you away from StackExchange, but Bodybuilding has the answer.
I'll just copy over the ones related to muscle building and fitness:
I'd say the increase in heart rate, and the incremental damage to the lungs will be most problem.
Also keep in mind that nicotine acts as a coronary vasoconstrictor and increases insulin resistance. I imagine the decreased blood flow might adversely effect your cardiac output despite the increased rate, or likely reduce your total potential cardiac output. I know it also does some peripheral vasoconstriction, potentially in muscle cells, the extent to which that is overcome by the metabolic hyperemia that comes with weight training but there is a good chance you're forcing your muscle cells into switching to anaerobic energy metabolism early than they should. (thus reducing force of contraction)
Also, decreasing insulin sensitivity is a bad thing if you are trying to put on muscle. Just ask any of those bodybuilders who inject the stuff. It is an "anabolic" hormone.
The improvement in lung function is probably more important than all the other stuff I just mentioned. Better lung function = better oxygenation to muscles during exercise = increased output
Buyer beware, I'm not a physiologist, and it's been a while since I studied it formally.