A rumored megamerger between pharmaceutical giants AstraZeneca and Bristol Myers Squibb is facing backlash on Wall Street — confusing analysts and spurring a significant stock sell-off. Bristol Myers’ top sellers include the immunotherapy Opdivo, the blood thinner Eliquis and the immune system regulator Orencia. And other so-called growth products like the schizophrenia medication Cobenfy, which Bristol Myers paid $14 billion to acquire, have yet to impress commercially. On one hand, Bristol Myers’ top products are under patent pressure. Bristol Myers did not respond to a BioPharma Dive request to comment.