Nicotine replacement therapy (NRT) is a medically approved way to treat people with tobacco use disorder by taking nicotine through means other than tobacco. It is used to help with quitting smoking or stopping chewing tobacco. It increases the chance of quitting tobacco smoking by about 55%. Often it is used along with other behavioral techniques. NRT has also been used to treat ulcerative colitis. Types of NRT include the adhesive patch, chewing gum, lozenges, nose spray, and inhaler. The use of multiple types of NRT at a time may increase effectiveness.

Common side effects depend on the formulation of nicotine. Common side effects with the gum include nausea, hiccups, and irritation of the mouth. Common side effects with the patch include skin irritation and a dry mouth while the inhaler commonly results in a cough, runny nose, or headaches. Serious risks include nicotine poisoning and continued addiction. They do not appear to increase the risk of heart attacks. There are possible harms to the baby if used during pregnancy. Nicotine replacement therapy works by reducing cravings caused by nicotine addiction.

They were first approved for use in 1984, in the United States. Nicotine replacement products are on the World Health Organization's List of Essential Medicines. They are available as generic medications.

Nicotine replacement therapy, in the form of gum, patches, nasal spray, inhaler and lozenges all improve the ability of people trying to quit tobacco products. Nicotine replacement therapy is as effective as medications, such as bupropion, in helping people quit smoking for at least six months. All forms of nicotine replacement therapy, including nicotine gum, patches, nasal spray, inhalers, and lozenges, have similar success rates in terms of helping people stop smoking. However, the likelihood that someone will stick to a certain treatment varies, with compliance being the highest with nicotine patches, followed by nicotine gum, inhalers, and nasal sprays. Using a few different nicotine replacement methods in combination may improve success rates in stopping tobacco use. Additionally, using nicotine replacement with counseling has been proven to improve tobacco abstinence rates. These other strategies include: creating a plan to quit and utilizing quit programs, a quit phone line, or app that provides tips and inspiration to help quit.

Using nicotine replacement therapy to quit smoking should be considered for people who are severely dependent on nicotine. People who are severely dependent include those who smoke: more than one pack per day, within five minutes of awakening, while ill, when they wake up in the middle of the night, to ease withdrawal signs and symptoms.

Nicotine replacement products are most beneficial for heavy smokers who smoke more than 15 cigarettes per day. There are not enough studies to show whether NRT helps those who smoke fewer than 10 cigarettes per day.

Evaluation of NRT in real-world studies produces more modest outcomes than efficacy studies conducted by industry-funded trials. The National Health Service (NHS) in England has a smoking cessation service based on pharmacotherapy in combination with counseling support. An Action on Smoking and Health (UK) (ASH) report claims that the average cost per life-year gained for every smoker successfully treated by these services is less than £1,000 (below the NICE guidelines of £20,000 per QALY (quality-adjusted life year). However, the investment in NHS stop smoking services is relatively low. A comparison with treatment costs for illicit drug users shows that £585 million is committed for 350,000 problem drug users compared to £56 million for 9 million users of tobacco. This is £6.20 for each smoker, compared to £1,670 per illegal drug user.

The claims for high efficacy and cost-effectiveness of NRT have not been substantiated in real-world effectiveness studies. Pierce and Gilpin (2002) stated their conclusion as follows: "Since becoming available over the counter, NRT appears no longer effective in increasing long-term successful cessation" (p. 1260). Efficacy studies, which are conducted using randomized controlled trials, do not transfer very well to real-world effectiveness. Bauld, Bell, McCullough, Richardson and Greaves (2009) reviewed 20 studies on the effectiveness of intensive NHS treatments for smoking cessation published between 1990 and 2007. Quit rates showed a dramatic decrease between 4-weeks and one year. A quit rate of 53% at four weeks fell to only 15% at one year. Younger smokers, females, pregnant smokers and more deprived smokers had lower quit rates than other groups.^{[citation needed]}