We hypothesized that during the Christmas season the safety profile and the toxicity of some drugs may be exacerbated. We therefore assessed and characterized changes in drug safety profiles over the Christmas period.

We performed a retrospective longitudinal analysis of adverse events reported in the World Health Organization (WHO) pharmacovigilance database between April 1st 2017 to March 31th 2023.

We extracted cases reported by the 5 main contributors’ countries of the WHO pharmacovigilance database with a Christmas tradition: USA, France, Germany, Italy and UK.

We analyzed 4,999,459 individual case safety reports from USA (n=3,498,961), France (n=419,018), Germany (n=398,763), Italy (n=251,641) and UK (n=431,076), reported between April 1st 2017 to March 31th 2023.

Monthly reports of adverse events were analyzed. Time trend, seasonal effect a Christmas effect (December–January) were explored.

We found 91 adverse events significantly more frequently reported during the Christmas period, independently after controlling for winter effect and general tendency. The main type of adverse events were psychiatric disorders, infections and skin and subcutaneous disorders. The highest numbers of attributable cases to Christmas were found for drug dependence, emotional distress, and drug withdrawal syndrome. The most involved drugs were oxycodone in psychiatric disorders (n=47,527), docetaxel in skin disorders (n=9440) and social circumstances (n=1940), olmesartan in gastrointestinal disorders (n=1263), fentanyl in cardiac disorders (n=929), adalimumab in infections (n=11,316) and immune system disorders (n=3781), and collagenase clostridium histolyticum in reproductive system disorders (n=318).

Our study shows that a range of drugs adverse events are more frequently reported at Christmas compared to other periods of the year, notably psychiatric disorders, infections, and skin disorders.