Merck & Co. (MRK) S-3ASR Automatic shelf registration

Exhibit 23(a)

CONSENT OF INDEPENDENT REGISTERED PUBLIC ACCOUNTING FIRM

We hereby consent to the incorporation by reference in this Registration Statement on Form S-3 of our report dated February 27, 2012 relating to the financial statements, and the effectiveness of internal control over financial reporting, which appears in Merck & Co., Inc.’s Annual Report on Form 10-K for the year ended December 31, 2011. We also consent to the reference to us under the heading “Experts” in such Registration Statement.

/s/ PricewaterhouseCoopers LLP

PricewaterhouseCoopers LLP

Florham Park, New Jersey

November 30, 2012