Nicotine

Nicotine is a naturally occurring stimulant found in tobacco and in the nightshade plant family, and it is the primary addictive ingredient in cigarettes, cigars, smokeless tobacco, and most vaping (e-cigarette) products. Most people who use tobacco do so regularly because they are addicted to nicotine. While nicotine itself drives addiction, much of the serious long-term harm of smoking comes from the many other chemicals in tobacco smoke; vaping devices deliver nicotine along with other chemicals and flavorings as an aerosol. Nicotine-replacement therapies (patches, gums, lozenges) deliver controlled doses of nicotine to help people stop smoking. Nicotine is legal and widely available, but its sale is regulated, including a federal minimum purchase age of 21 in the United States.

Nicotine works by binding to nicotinic acetylcholine receptors in the brain. This triggers the release of several neurotransmitters, most importantly dopamine in the brain's reward circuits, producing a brief, mild pleasure and reinforcing repeated use. A short-lived surge of endorphins can cause a brief, slight euphoria, and nicotine can temporarily increase alertness, attention, and short-term memory while reducing appetite. Because the rewarding effect is brief, users tend to dose repeatedly throughout the day, which strongly reinforces dependence. Outside the brain, nicotine stimulates the cardiovascular system, increasing heart rate, blood pressure, and the heart's oxygen demand.

Nicotine commonly produces a brief feeling of alertness, mild stimulation, and relaxation, along with reduced appetite. Some people feel a faster heartbeat or mild anxiety, nausea, or lightheadedness, especially when they are new to it or take a higher dose. Tolerance develops quickly, and regular users often feel that nicotine simply relieves the discomfort of withdrawal rather than producing a noticeable high. Withdrawal symptoms can begin within hours of the last use and include irritability, intense craving, anxiety, difficulty concentrating, restlessness, sleep problems, and increased appetite.

Nicotine is highly addictive — this is its central risk, because addiction keeps people using tobacco products whose other components cause cancer, lung disease, heart attack, and stroke. Nicotine itself stresses the cardiovascular system by raising heart rate and blood pressure. It is genuinely dangerous to children and pets: concentrated liquid nicotine (e-cigarette refill fluid) can cause severe poisoning or death if swallowed, and even small amounts matter for a small body, so these products must be kept locked away. Nicotine exposure during pregnancy can harm fetal development, and adolescent use can affect the developing brain. Symptoms of nicotine poisoning include nausea, vomiting, rapid heartbeat, seizures, and difficulty breathing. If poisoning is suspected, contact Poison Control at 1-800-222-1222, or call 911 in an emergency. For help quitting, the SAMHSA helpline is 1-800-662-4357, and effective treatments exist, including nicotine-replacement therapy and prescription medications.