Rising insulin costs are drawing outrage from diabetes advocates, leading to calls for greater transparency and federal oversight of the market for a drug that helps more than 7 million Americans.

Three companies — Eli Lilly, Sanofi and Novo Nordisk — control 99 percent of the world’s insulin, and advocates have been asking them to explain their pricing. According to the American Diabetes Association, the average price of insulin nearly tripled between 2002 and 2013.

The price for a vial of one the most popular insulin brands, Humalog, increased from $21 in 1996, to $35 in 2001, to $234 in 2015, to $275 in 2017. There are no generic forms of insulin on the market, but there are some cheaper “biosimilar” versions.

“Americans need Congress to take action to ensure a vibrant, competitive insulin market that serves consumers instead of drug company CEOs. Insulin is not a luxury. It is required for life,” said Ben Wakana, executive director of the advocacy group Patients for Affordable Drugs.

Read more at The Hill.