Nicotine is a highly toxic chemical. While in rats, a dose of 50 mg per kg is lethal, in mice the median lethal dose is around 3 mg per kg weight. In humans, the median lethal dose is 0.5 to 1.0 mg/kg or around 40 to 60 mg in an average human.
This low lethal dose makes nicotine more toxic than many other compounds including even alkaloids such as cocaine which has a median lethal dose of 95.1 mg per kg in mice.
Nicotine overdosing
Despite its high toxicity, a person cannot overdose on nicotine just by smoking the substance. Overdose, however, can occur if a person uses too many nicotine patches or chews too much nicotine gum or chewing tobacco as well as smoking.
As nicotine can be absorbed into the bloodstream easily through the skin, if an extremely high concentration of nicotine is spilt on the skin, this can lead to toxicity and death.
Nicotine as a carcinogen
The association between smoking and cancer has been established in numerous studies over the years. However, nicotine has not yet been clearly identified as a cancer causing agent in cigarettes and is not yet officially listed as a carcinogen.
Although there is no solid evidence supporting that nicotine is a carcinogen, the carcinogenic potential of the substance has been demonstrated in various animal and cell culture studies over the last ten years.
It has been shown that nicotine activates MAP kinases, increases adrenergic signalling in bowel cancer and disrupts apoptosis or programmed cell death. This cell death actually clears the body of cells that have been damaged or have undergone mutations.
Impairment of apoptosis means damaged and altered cells remain, creating a pathway for cancers to develop. Nicotine has also been shown to promote angiogensis or the formation of new blood vessels which can help a tumour to survive and grow.
Further Reading
Feedback loop involving estrogen linked to women's higher propensity to nicotine addiction