The biggest moneymaker for Regeneron (REGN +0.93%) is Eylea, an eye disease drug that the company makes in collaboration with Bayer (OTC:BAYR.Y). All net sales from Eylea in the U.S. are awarded to Regeneron, and the company splits the revenue earned from markets outside the U.S. with Bayer.
Regeneron also has a lucrative partnership with Sanofi (SNY +0.50%), another life sciences and pharmaceutical company. Together, the two companies are marketing and selling the autoimmune disease drugs Dupixent and Kevzara, the cancer drugs Libtayo and Zaltrap, and the cholesterol drug Praluent.