Nicotine addiction, or nicotine dependence is an addiction to tobacco products caused by the drug nicotine. Nicotine dependence means you can't stop using the substance, even though it's causing you harm. Nicotine produces physical and mood-altering effects in your brain that are temporarily pleasing. These effects make you want to use tobacco and lead to dependence. At the same time, stopping tobacco use causes withdrawal symptoms, including irritability and anxiety.