Smoking, and the intake of hundreds (?)
of carcinogens ie dangerous. Nicotine is addictive but it’s hard to say if it’s dangerous by itself. There is some data suggesting that it is a cocarcinogen, or tumor promoter, but no evidence to suggest it by itself is a true carcinogen. There are some benefits in moderation too. The danger is with the addiction AND intaking nicotine from sources that are carcinogenic.