Hello again Dr.Garcia! I wrote to you another day about a surgery I'm about to do and my smoking habits. I appreciate your answer really much but now I got one more question. What other substances are dangerous relative to a surgery other than tobacco, nicotine, carbon monoxide? I will quit tobacco smoking but I wonder about herbal smokes, without nicotine and tobacco? Is that alright? Not for daily use but for blending my marijuana, at weekends for example? Does marijuana have nicotine in it? I hope you can answer this question as well. Thank you!