BackgroundHealthcare professionals are exposed to advertisements for prescription drugs in medical journals. Such advertisements may increase prescriptions of new drugs at the expense of older treatments even when they have no added benefits, are more harmful, and are more expensive. The publication of medical advertisements therefore raises ethical questions related to editorial integrity.MethodsWe conducted a descriptive cross-sectional study of all medical advertisements published in the Journal of the Danish Medical Association in 2015. Drugs advertised 6 times or more were compared with older comparators: (1) comparative evidence of added benefit; (2) Defined Daily Dose cost; (3) regulatory safety announcements; and (4) completed and ongoing post-marketing studies 3 years after advertising.ResultsWe found 158 medical advertisements for 35 prescription drugs published in 24 issues during 2015, with a median of 7 advertisements per issue (range 0 to 11). Four drug groups and 5 single drugs were advertised 6 times or more, for a total of 10 indications, and we made 14 comparisons with older treatments. We found: (1) ‘no added benefit’ in 4 (29%) of 14 comparisons, ‘uncertain benefits’ in 7 (50%), and ‘no evidence’ in 3 (21%) comparisons. In no comparison did we find evidence of ‘substantial added benefit’ for the new drug; (2) advertised drugs were 2 to 196 times (median 6) more expensive per Defined Daily Dose; (3) 11 safety announcements for five advertised drugs were issued compared to one announcement for one comparator drug; (4) 20 post-marketing studies (7 completed, 13 ongoing) were requested for the advertised drugs versus 10 studies (4 completed, 6 ongoing) for the comparator drugs, and 7 studies (2 completed, 5 ongoing) assessed both an advertised and a comparator drug at 3 year follow-up.Conclusions and relevanceIn this cross-sectional study of medical advertisements published in the Journal of the Danish Medical Association during 2015, the most advertised drugs did not have documented substantial added benefits over older treatments, whereas they were substantially more expensive. From January 2021, the Journal of the Danish Medical Association no longer publishes medical advertisements.