Nicotine Replacement Therapy (NRT) is a way of delivering nicotine to address cravings and withdrawal symptoms without taking in all the harmful chemicals found in tobacco smoke. Nicotine replacement therapy is available in many forms, and these can be prescribed by a doctor, all in an effort to help smokers give up tobacco completely. The products work a bit differently in terms of how and where the nicotine is absorbed, how much is delivered, and in what time frame.