There is little evidence as to why this association exists; however, it has been hypothesized that those who are predisposed to smoking are also predisposed to suicide, that smoking causes health problems which subsequently make people want to end their life, and that smoking affects brain chemistry causing a propensity for suicide.
Vi ved ikke meget om, hvorfor forbindelsen findes, men der er en teori om, at de, der er prædisponeret for at ryge også er det for at begå selvmord, eller at rygning giver helbredsproblemer, som fører til, at mange vil begå selvmord, og at rygning påvirker hjernens kemi, så den får hang til selvmord.