Pfizer’s plan to market an over-the-counter version of its statin Lipitor, once the world’s best-selling drug, is over.

The drugmaker said Wednesday that the Phase-III actual-use trial had failed to meet the primary objectives, and the program was terminated after Pfizer executives discussed the results with FDA officials.

The news brings to an end Pfizer’s long-running attempt, first reported in 2011, to recoup losses from its former best-selling drug through an OTC switch. In stopping the program, Pfizer also joined the ranks of Merck and Bristol-Myers Squibb, two other drugmakers that were unable to make their once-popular statin brands available without a doctor’s prescription.

Manufacturers seeking to switch prescription drugs to OTC products conduct actual-use studies, which evaluate how consumers will respond to a prescription product in an OTC environment. That data is presented to the FDA to determine whether the prescription requirements are necessary before the company files a supplement to a new drug application.

Pfizer’s actual-use study, which began in October 2013 and enrolled 1,311 patients, had tested two primary outcomes measures: how many patients had their LDL levels checked after taking the drug, and how many patients, after getting LDL levels checked, took appropriate action based on test results. The trial also looked at how many patients contacted a doctor or pharmacist before starting to take the OTC version of the drug.

Earlier this year a Pfizer executive had told investors that the trial was completed in December and that “the results of the study will inform next steps and timelines for potential NDA filing.” The drugmaker later released the results of a poll looking at consumer and physician perceptions and behaviors related to OTC products.

Lipitor, which lost patent exclusivity in 2011, generated $509 million in global sales in the second quarter of 2015, down from the $543 million it brought in during the same period a year ago. The drug brought in sales of nearly $13 billion at its peak in 2006. But the company later had mixed success with an authorized generic program for Lipitor.

For drug firms seeking to extend revenue for their once-protected brands, Rx-to-OTC switches have not proven a reliable lifecycle tactic. While several makers of prescription allergy drugs have reported success converting their pills to prescription-free status over the years, sellers of statins have had a tougher time.