Off-label prescribing can be defined as “prescribing currently available and marketed medications for an indication (eg, a disease or a symptom) that has never received United States Food and Drug Administration (FDA) approval.”1 The practice is “legal and common…one in five prescriptions written today are for off-label use.”2 However, despite its frequency, off-label prescribing remains a controversial practice, as it is a “potentially important contributor” to adverse drug events (ADEs).3  

A recent study by Eguale and colleagues3 examined the electronic health records of a cohort of 46,021 patients who received 151,305 incident prescribed drugs in Quebec primary care clinics over a five-year period. The study followed the dispensed prescription from the date the prescription was issued until the date that drug use was discontinued, the end of treatment, or the end of follow-up.  The main outcome was “adverse events in off-label use” and took into account whether the drug use was or was not supported by scientific evidence.3 According to the authors, this was the first major systematic investigation of the impact of “real-life off-label  use” on adverse events.

Review of the patients’ records revealed that off-label use was reported in 17,847 (11.8%) of prescriptions. In 14,431 of these cases (80.9%), the off-label use lacked scientific evidence. There was a total of 3,484 ADEs, with an incidence rate of 13.2 per 10,000 person-months. There was a higher rate of ADEs for off-label use (19.7 per 10,000 person-months) than for on-label use (12.5 per 10,000 person-months [AHR 1.54; 95% CI, 1,37-1,72]).