WOONSOCKET — Moody’s Investors Service lowered its outlook on CVS Caremark Corp. on Tuesday, citing the struggles of the company’s pharmacy-benefits management (PBM) division.

Moody’s lowered CVS’ outlook from “positive” to “stable” — meaning the agency is unlikely to raise CVS’ credit rating — but affirmed the company’s current ratings, including its senior unsecured rating of Baa2, Marketwatch reported.

CVS disclosed earlier this month that the PBM unit has lost $4.8 billion in contracts for 2010 because of major clients switching to other providers.

“The change in outlook to stable from positive reflects Moody’s view that a near term upgrade is unlikely given the time it will take for CVS Caremark to demonstrate that it has adequately addressed the issues that led to the significant contract losses and lost market share at its pharmacy services division,” the ratings agency said in a statement quoted by Marketwatch.

However, Moody’s said the PBM unit’s issues were not likely to have a major effect on the company’s credit.