Ashtray. Ashtray containing cigarette butts and a lit cigarette. Cigarette tobacco contains a variable amount of nicotine, a toxic chemical, and several cancer causing substances. There is a direct link between the amount of tobacco used, and the likelihood of cancer. Three reagents in tobacco are particularly harmful. Nicotine is extremely addictive and stimulates the release of adrenaline, leading to increased blood pressure. Tar in tobacco produces chronic irritation in the lungs which can cause lung cancer. Carbon monoxide in smoke passes into the bloodstream where it can lead to coronary thrombosis.