Addiction is a mental and physical condition caused by the interaction of drugs and the organism characterized by a compulsion for occasional or regular enjoyment of substance of abuse, to create a feeling of pleasure or to avoid discomfort due to the absence of substance of abuse. There is an increasing proportion of addict in the population. Most commonly used addictive substances are tobacco and alcohol. Substance of abuse cause changes of tissues inside the mouth and the doctors of dental medicine are first who can note that, which makes it necessary to educate them about the various changes that has the use of various addictive substances. Substance of abuse are tobacco, alcohol and drugs. Tobacco causes malignant and non-malignant changes in the oral cavity, has a vasoconstrictive effect and is a major risk factor in the development of malignant lesions of the oral cavity together with alcohol. Alcohol acts dehydrating to the mucous membranes of the oral cavity, has negative interactions with 150 different kinds of medications which requires caution when prescribing medications. Psihodepressing drugs mask the pain and make it difficult to anesthetizing addicts, psychostimulant drugs cause a feeling of euphoria. Cocaine can lead to perforation of the nasal septum and palate, while methamphetamine results in a "meth-mouth" which includes extensive caries lesions. Cannabinoids may cause the development of oedema uvula, hallucinogens complicate management with patients due to the phenomenon of hallucinations and delusions, and the consumption of inhalatory addictive substances are diagnosed by finding the wounds and stains around the mouth. It is necessary to have individually and empathetic approach to each patient in order to develop a sense of confidence and better cooperation, identify changes occurring on the oral mucosa, to make a differential diagnosis of thelesions and to start the treatment timely.