Heroin, also known as diacetylmorphine, is a product of acetylation of morphine. In general, it is no longer used in medicine, but has become an illicit drug that causes, for example, euphoria and sedation. It can be administered in different ways, including intravenously. There are studies indicating that using heroin can cause brain structure changes in, for example, the nucleus accumbens, which is part of the brain reward system. The aim of this paper is to review studies on structural brain changes in heroin dependents. A Pub-Med search was conducted using keywords such as “brain changes heroin” and “heroin and gray matter volume reduction”. From 10 papers that covered the topic, 7 were selected for the review. Publications not available in English were excluded. Studies have shown that there are changes in the morphology of brain structures in heroin addicts. Heroin dependents have reduced gray matter volume as well as gray matter density in particular parts of the brain. However, using other substances, including nicotine, can influence the results and must be taken into consideration when interpreting them. Structural brain changes that are described in heroin addicts can be related to changes in their behavior. There is a need for other studies in this matter, including many different covariates, for example other substance use, receiving methadone maintenance treatment, or duration of using heroin.