Key:

+++ high, well-established risk

++ causal role accepted by leading health authorities

+ plausible risk, but evidence is not definitive

- not a probable risk

Health effects of primary smoke constituents

substance addiction cancer heart disease lung disease pregnancy problems

Nicotine +++ - ++ +

Carbon monoxide - - +++ ++ +++

Tar (particulate residue) + +++ ++ +++ undetermined