Nicotine
Health: Nicotine is extremely addictive and causes withdrawal effects. Nicotine has been proven to cause lung disease and is extremely carcinogenic. Cigarettes are responsible for over 5 million deaths per year.
Actually, that is not quite right. Nicotine dependence is a serious problem, and not just placebo. It is also very toxic (lethal dose: 0.5-1.0 mg/kg body mass)
BUT: it has
no scientifically proven carcinogenic effect for humans, and does
not cause lung disease. It does, however, cause tumor cells to get more nutrients, thereby making it grow easier. But it doesn't cause the cancer.
HOWEVER, all of those other chemicals commonly found in cigarettes pack a punch:
- HCN, hydrogen cyanide, is a very poisonous substance, contained in cigarette smoke. German WW2 officers used it to commit Self Delete.
- CO, carbon monoxide, will bind itself to hemoglobin in your blood, which is responsible for oxygen transport. To much of it will make you suffocate from inside.
- Tar, the stuff you have in asphalt. Not good for your lungs.
- Benzole, highly carcinogenic.
- Heavy metals such as Lead, Cadmium and Polonium. These are highly toxic and also carcinogenic. (Polonium is radioactive, too :S)
- NO, NO2, NH3. just for the added fun.
All these chemical are contained in cigarette smoke (to greater or lesser extent)
But saying that nicotine does all the damage is very wrong :P