Tobacco is addictive because it contains a psychoactive substance called nicotine, which is a highly addictive stimulant drug. When a person inhales smoke from tobacco products like cigarettes or cigars, the nicotine is absorbed into the bloodstream through the lungs and quickly travels to the brain. Once in the brain, nicotine activates the release of the neurotransmitter dopamine, which is associated with feelings of pleasure and reward. This creates a sense of euphoria and well-being that reinforces the desire to use tobacco products again in the future.