Traders gather at the post of Pfizer on the floor of the New York Stock Exchange in New York.

J.P. Morgan downgraded Pfizer shares to neutral from overweight on Tuesday, warning clients that the stock's rally will likely slow after climbing more than 22 percent this year.

"We clearly have seen a positive shift in Pfizer's narrative, which is now focused on the re-acceleration of the company's top and bottom line growth beyond 2020," J.P. Morgan's Chris Schott said in a note.

"However, with the company now trading in line with peers and the broader market, we see this improved core story as better reflected in valuation," Schott added. "And with further upside to shares likely tied to either additional pipeline success or positive new launch momentum (largely 2020+ events), we are moving to the sidelines."

Shares of Pfizer closed down 0.9 percent at $44.01 a share. J.P. Morgan stuck to its $46 price target on Pfizer. Investors have boosted Pfizer shares amid a broader sell-off in the market.