Nicotine is relatively harmless, all the harm from smoking comes from tobacco smoke.

Public Health England, Guidance: Health matters: stopping smoking – what works?, December 2019

Key Points:

The widespread misconception among smokers and health professionals that most of the harm of smoking comes from the nicotine is one of the greatest obstacles faced by Public Health England.
Nicotine replacement therapy (NRT) is a safe form of treatment and licensed for use even in pregnancy and for people with cardiovascular disease.
Nicotine increases heart rate and blood pressure, and has a range of local irritant effects, but is not a carcinogen.
It is the tar and carbon monoxide in cigarette smoke, along with more than 400 other toxins, that causes almost all of the harm of smoking.
The three main causes of mortality from smoking are lung cancer, Chronic obstructive pulmonary disease (COPD) and cardiovascular disease, none of these are caused by nicotine.
Using NRT or e-cigarettes (vaping) makes it one and a half times as likely a person will succeed in quitting.