Communications about the safety and effectiveness of human drugs can influence patients' and prescribers' perceptions and behaviors, which in turn can affect the public's health more broadly. We conducted a critical review of the literature on the unintended effects from communicating information to the public about safety issues with prescription and over-the-counter drugs. We searched PubMed for peer-reviewed studies published from 1990 to 2017 where study authors reported probable unintended effects of communicating drug safety. The types of communications included in these studies were news reports, direct-to-consumer advertisements, and those released by government agencies. Among the 26 studies identified, the most commonly reported unintended effects were decreased drug use or discontinuation. Other unintended effects included spillover to populations not targeted by the communications (e.g., discontinuation of antidepressants among adults following communications concerning use among youth), shifts in clinical diagnoses (e.g., fewer diagnoses of depression), increased use of alternative therapies, and other undesirable behaviors (e.g., possible increased suicide attempts because antidepressants were discontinued). Limitations to the literature include the inability to establish causation or to isolate the effects of multiple communication sources and messages. Further, because the intended effect of many communications was not known, our study was limited by challenges in defining some effects as unintended. Most studies used health insurer claims data to identify unintended effects of communications, which provide an incomplete picture; few used self-reported or other methodologies that could help illuminate the reasons underlying the effects observed in the claims data. Best practices for communicating about the potential benefits and harms of drugs in a manner that minimizes negative unintended effects are needed to protect and improve public health.