UnitedHealth Group’s Optum is acquiring Diplomat Pharmacy in a $300 million deal, officials for both companies announced Monday.

Diplomat, a provider of specialty pharmacy and infusion services, had been struggling to compete with larger pharmacy benefits companies and saw its stock value drop 57% since the start of the year.

UnitedHealth Group will fold Diplomat into its OptumRx pharmacy-benefits unit, already one of the nation’s largest.

Diplomat brings expertise in managing specialty medications that treat patients with complex diseases, such as oncology and immunology. UnitedHealth said in a release that the combination will “support improved health outcomes and reduced prescription drug costs,” although critics have routinely blamed large PBMs for soaring prices.

“This combination will expand the innovative specialty pharmacy and infusion solutions OptumRx can offer to the consumers and clients we serve, helping ensure people get the right medications and services at the right time, in the right setting,” said John Prince, chief executive officer of OptumRx.

The transaction was unanimously approved by Diplomat’s board of directors. The company was founded in 1975 as a neighborhood pharmacy and entered the PBM market just two years ago when it purchased LDI Integrated Pharmacy Services and National Pharmaceutical Services.

OptumRx manages the prescription drug benefits of commercial, Medicare, Medicaid and other government health plans through a national network of 67,000 community pharmacies.