OBJECTIVES: Diabetes mellitus is one of the most prevalent and costly diseases in the US. Insulin is an essential drug for many diabetes patients. We assessed trends in prices of injectable insulin in the period January 1984-January 2020.

METHODS: Data for insulin marketed in the US during the period January 1984- January 2020 was derived from the FDA databases; and the wholesale acquisition cost (WAC) from the RedBook (IBM Micromedex). We converted prices to 30-day-supply (30-DDD). Prices increases were compared with the consumer price index (CPI). Descriptive analyses were conducted in this study.

RESULTS: The WAC of the first human short-acting insulin and the first intermediate-acting insulin increased from $12.42 on January 1, 1984, to $178.44 per 30-DDD on January 1, 2020, representing a price increase 6.4 times higher than the CPI. Similar 30-DDD WAC increases were observed for intermediate-acting insulin ($12.42 in 1987 to $178.44 in 2020, 6.4 times higher than the CPI increase), rapid-acting insulin ($24.98 in 1997 to 329.64 in 2020, 8.4 times higher than the CPI increase), long-acting insulin ($43.51 in 2002 to $340.27 in 2020, increase 5.5 times higher than the CPI), short and intermediate-acting premixed insulin (13.68 in 1990 to $178.44 in 2020, 6.7 times higher than the CPI increase), and rapid/intermediate-acting premixed insulin ($47.70 in 2001 to $341.64 in 2020, 5 times higher than the CPI increase). Prices varied by form (vial, cartridge, pen, syringe) and strength. Follow-on and authorized generics entered the market at a median of 50% the reference insulin price. Prices of brand insulin products competing in the same class had a very similar price trend in the period of analysis.

CONCLUSIONS: The price of insulin increased substantially during the period 1984-2020 threatening the affordability of these life-saving drugs. Authorized generics and follow-on products reduced in half the listed prices.