The WHO calls tobacco “the single most preventable cause of death in the world”—but cigarettes may also provide a handful of paradoxical, if pyrrhic, health benefits: Smoking will probably take years off your life, but certain things in tobacco smoke may actually do the body good. Here’s what science has to say about the smoker’s paradox.
Smoking Alleviates Ulcerative Colitis but Inflames Crohn’s Disease
Broadly speaking, smoking worsens your health. But for some people who suffer from inflammatory bowel disease (IBD), smoking seems to relieve their worst symptoms.
A positive effect: There are not a lot of treatment centers for castor oil sippers. See the rest of the answer for why smoking has this covered.
The positive effect occurs quickly after behaviour: Anti-depressants are unlikely to be abused because the subject takes one and then 3-4 weeks later starts to feel subtly better - the feel-good and the action don't have a strong connection. It's hard to find a faster way to deliver a drug than to inhale it.
The positive effect has a brief duration: If your new drug makes people happy for the rest of their life they will never need to take it again. The more quickly it wears off the more opportunity for them to re-take it and loop through the associations of number two. Nicotine has a half-life of about an hour.
The positive effect has negative side effects alleviated by reapplication. Whether it's a heroin user "getting well" or a frat boy "postponing a hangover", if the drug punishes you for not taking it again, you'll get your users attention. Try to arrange it so ingestion causes not only pleasure but relief. Nicotine withdrawal is awful - it feels, as someone once said, like being a cat with your fur brushed the wrong way in a static storm.