Question: What should I do when my father asks me to buy him cigarettes? Do I listen to him because of kibbud av or refuse because he’s damaging his health?
Answer: The consensus of contemporary poskim is that it absolutely forbidden to smoke (See Minchas Shlomo 2:58:6, Teshuvos Vehanhagos 4:115; Shevet Halevi 10:295).
Many poskim who initially took a more lenient stance, later forbade smoking explicitly. R’ Ovadia Yosef (Yabia Omer 5:OC 39) and R’ Eliezer Waldenberg (Tzitz Eliezer 1:20:3) initially took a more lenient stance, though later (Halichos Olam 1:p265 and Tzitz Eliezer 15:39) they both explicitly forbade it.
Many who smoke quote R’ Moshe Feinstein (Igros Moshe YD 2:49) who wrote (in 1964) that while one shouldn’t smoke, he couldn’t say that it was halachically forbidden. R’ Moshe himself took a stricter stance in his later Teshuvos (Igros Moshe CM 2:18; 76; See too Rivevos Ephraim 8:586).R’ Moshe Stern (Be'er Moshe 1:60:10) answers your question. As smoking will damage his health, he is asking you to do something that runs contrary to the Torah. In such a case, you have to politely decline.