Insulin manufacturers Eli Lilly and Co., Novo Nordisk, and Sanofi will have to answer to lawmakers on why insulin prices have almost doubled between 2012 and 2016.

House Energy and Commerce Committee Chairman Frank Pallone, Jr. (D-N.J.) and Oversight and Investigations Subcommittee Chair Diana DeGette (D-Colo.) sent letters to the drugmakers Jan. 30 asking executives to provide details on average prices, net profits, and changes or modifications they’ve made to products that could justify price increases.

Company leaders will also have to answer whether they’ve engaged in any regulatory stalling tactics or pay-for-delay deals to keep generic versions of their...