It is not possible to precisely diagnose death related to drug overdose based on pathologic criteria only, because there are no drug-specific lesions. Although, one may notice acute macroscopic and microscopic changes which, by their combination and together with elements collected from the death scene investigation, orientate the forensic pathologists interpretation towards the possibility and probability of such cause of death, which is to be confirmed by toxicological analysis. Pulmonary changes follow a lobular distribution, with congestive and edema areas alternating with acute emphysema. Edema liquid is protein-rich and sometimes we also find hemorrhagic edema. Increased lung density correlates with the severity of the pulmonary edema. Alveolar wall inflammatory changes progress in time after the last injection and the intensity of the alveolar reaction depends upon the nature and amount of the injected drugs. Embolization, vascular inflammatory processes and perivascular granulomas may cause death directly, if drugs designed for oral medication are injected intravenous. Chemical acute pneumonitis develops after aspiration of material with pH lower than 2.4. In its progression, the "narcotic" lung appears more than three hours after the heroin overdose injection and up to about twelve hours.