Drug use for both therapeutic and recreational purposes is very widespread in most societies. The range of drugs used, the variations in response to these drugs and other health and behavioral confounders mean that drug use may be an important contributor to individualized periodontal diagnoses. In this narrative review, we review the main reported effects of drugs on the periodontal tissues and periodontal disease processes. Although some of the more common adverse drug reactions on periodontal tissues are well described, in many other cases the evidence for these drug effects is quite limited and based on small case series or isolated reports. Prescription drugs are responsible for a range of effects, including drug‐induced gingival overgrowth and increased gingival bleeding, and influence periodontal inflammation and periodontal breakdown. The effects of recreational drugs on the periodontal tissues is less well researched, perhaps for the obvious reason that assembling large cohorts of recreational drug users presents particular challenges. Use of nearly all of these substances is associated with poorer periodontal and dental health, although there is almost certainly a large degree of behavioral confounding in these findings. Overall, further studies of adverse drug reactions on the periodontal tissues are required as this continues to be an important and increasing factor in periodontal health determination.