Tar is the material produced by burning tobacco. It can damage lungs & cause cancer. It is also found in marijuana cigarettes. Nicotine is an alkaloid from plants of the nightshade family. It acts as a stimulant, which leads to addiction. In brief: Tar/Nicotine. Tar is the material produced by burning tobacco. It can damage lungs & cause cancer. It is also found in marijuana cigarettes. Nicotine is an alkaloid from plants of the nightshade family.