Jim Chanos just slammed 2 pharma companies in a presentation about their 'murky alliance'

ReutersJim Chanos, founder of Kynikos AssociatesJim Chanos just presented his short thesis for Mallinckrodt Pharmaceuticals, a company that generates most of its revenue from one drug - Acthar.

At the same time, he slammed the company that exclusively distributes Acthar for Mallinckrodt, Express Scripts.

Express Scripts is a pharmacy benefit manager, which means it acts as the gatekeeper between drug companies and payers.

"This alliance may lead to performance enhancing drug prices," Chanos said, "but it could give investors the blues."

That is because the Centers of Medicare and Medicaid have noticed that Acthar is the most expensive drugs it pays for. Acthar was the only non-life saving drug on its list of the top 20 most expensive drugs of 2015.

As we've written before, Washington is circling around PBMs. Politicians on both sides of the aisle want to know more about the opaque way they control pricing and the way they help patients pay co-pays for expensive drugs. Express Scripts and Mallinckrodt have both told their shareholders that the Feds are looking into these programs.

Raul Hernandez contributed to this story.