Security of supply of medicines is fundamental to ensure health for all. Furthermore, improving access to medicines is included in sustainable development goal 3. However, the concept of security of supply has mostly been applied to food, water and energy. Diversity of supply, vulnerability to disruption, expenditure, infrastructure, stability of exporting countries, ownership of production, price stability, access and equity, affordability, intellectual property, safety and reliability of supply, and countries' capacity to adapt to market changes are all elements of security of supply. Based on these elements, we assessed security of supply for insulin, since access to insulin is a global problem. We found that three multinational companies, in Denmark, France and Germany, control 99% of the value of the global insulin market. Prices and affordability of insulin and access to it vary considerably between countries. Some countries are vulnerable to insulin shortage because they import insulin from only one source. Many countries spend large amounts of money on insulin and costs are increasing. Some countries lack an adequate infrastructure for procurement, supply chain management and distribution of insulin. Applying the security of supply concept to insulin showed that diversification of suppliers needs to be fostered. Global health actors should adopt a security of supply approach to identify medicines that are susceptible to supply issues and address this concern by strategic promotion of local production, strengthening regulatory harmonization, and adding local products to the World Health Organization's programme on prequalification of medicines.