To audit the transparent and open science standards of health and medical sciences journal policies and explore the impact of the COVID-19 pandemic. Repeat cross-sectional study. 19 journals listed in Google Scholar's Top Publications for health and medical sciences. Blood, Cell, Circulation, European Heart Journal, Gastroenterology, Journal of Clinical Oncology, Journal of the American College of Cardiology, Nature Genetics, Nature Medicine, Nature Neuroscience, Neuron, PLoS ONE, Proceedings of the National Academy of Sciences, Science Translational Medicine, The British Medical Journal, The Journal of the American Medical Association, The Lancet, The Lancet Oncology, and The New England Journal of Medicine. We used the Transparency and Openness Promotion (TOP) guideline and the International Committee of Medical Journal Editors (ICMJE) requirements for disclosing conflicts of interest (COIs) to evaluate journals standards. TOP scores slightly improved during the COVID-19 pandemic, from a median of 5 (IQR: 2-12.5) out of a possible 24 points in February 2020 to 7 (IQR: 4-12) in May 2021, but overall, scores were very low at both time points. Journal policies scored highest for their adherence to data transparency and scored lowest for preregistration of study protocols and analysis plans and the submission of replication studies. Most journals fulfilled all ICMJE provisions for reporting COIs before (84%; n = 16) and during (95%; n = 18) the COVID-19 pandemic. The COVID-19 pandemic has highlighted the importance of practising open science. However, requirements for open science practices in audited policies were overall low, which may impede progress in health and medical research. As key stakeholders in disseminating research, journals should promote a research culture of greater transparency and more robust open science practices.