I believe (this being based on years of looking into this for my edification) that what is "sin" or wrong to one unless it is very explicitly spelled out in the scripture as sin, is subject to the convictions of each individual person. You say your wanting a christian opinion but I am gonna give you mine anyways.
I myself am a backslidden recovering alcoholic, if and when I decide to trust God once again and re-convert back (its just my view), I know that I can never ever touch alcohol again, if I were to, I would be sinning. This I feel. But I know pastors and many other "good" christians that can have a beer or a glass of wine at dinner and do I think they are sinning? Nope. not at all. Its in moderation and the person can handle the drink without giving in to excessiveness.
As far as smoking/pot - I have my own personal views but I know those who are christians, truly believe and desire to live and love God and they smoke cigaretts and I have my serious doubts they are hell bound. The church organization I walked out of in '82 sais differently. (a little thing called "Holiness Standard" that was forced on us folks. Long hair and dresses only on women, cut hair on men, no make up, jewely, no tv, no alcoholc, no "devil" music, etc etc etc. yep. its what they believe. And I use to endorce/embrace this same stuff until i walked out. Now I see things a tad differently).
The Pot question for me is subjective to my personal views (or "convictions" as the christians would say). I smoked enough herb in my life to make me wonder how I ever returned to reasonable normalcy. Again, I would have to say iuts subjective to the person and their walk with God.
The only verse that I was ever aware of in the New Testament is the one in 1 Cor 3:16,17 about your bodyu being a temple of the living God and to defile it, etc etc.... The only other ones I can think that some can use as their argument agianst drinking and smoking tobacco/pot would be the verses that eptain mainly to holiness or one's walk - "let not your good be evil spoken of" or "avoid all appearance of evil", etc.
Not saying I subscribe to the interpretations that others would on these verses but I know they can be and have been used to disuade others from drink/smoke as a christian.
But all this is just my take on the topic and my personal views/opinions based on years of looking into it myself. I say its to the individual and his/her personal walk with God whether it would be sin or not. Some cant listen to certain genres of music without the temptation of the past, some cant wear certain clothes/dress certain ways, some have other personal retrictions on their lives based on their faith and walk that wouldnt bother or aply to someone else.