The WHO Model List of Essential Medicines is revised every 2 years to ensure it reflects the latest evidence on the safety, efficacy, and cost-effectiveness of medicines. This frequency allows for timely updates in response to emerging health challenges, new therapeutic options, and changes in disease patterns worldwide. Regular revisions help guide healthcare systems in selecting the most appropriate and essential medicines to meet the priority health needs of their populations. Thus, a biennial update balances the need for current guidance with practical review cycles.

Reference: WHO Model List of Essential Medicines, World Health Organization, Latest Edition.