Before Missouri put a prisoner to death on Wednesday, for example, it refused to say in court whether the lethal barbiturate it used, pentobarbital, was produced by a compounding pharmacy or a licensed manufacturer. Akorn, the only approved company making that drug, has tried to prevent its use in executions.

Pfizer’s decision follows its acquisition last year of Hospira, a company that has made seven drugs used in executions including barbiturates, sedatives and agents that can cause paralysis or heart failure. Hospira had long tried to prevent diversion of its products to state prisons but had not succeeded; its products were used in a prolonged, apparently agonizing execution in Ohio in 2014, and are stockpiled by Arkansas, according to documents obtained by reporters.

Because these drugs are also distributed for normal medical use, there is no way to determine what share of the agents used in recent executions were produced by Hospira, or more recently, Pfizer.

Campaigns against the death penalty, and Europe’s strong prohibitions on the export of execution drugs, have raised the stakes for pharmaceutical companies. But many, including Pfizer, say medical principles and business concerns have guided their policies.

“Pfizer makes its products to enhance and save the lives of the patients we serve,” the company said in Friday’s statement, and “strongly objects to the use of its products as lethal injections for capital punishment.”

Pfizer said it would restrict the sale to selected wholesalers of seven products that could be used in executions. The distributors must certify that they will not resell the drugs to corrections departments and will be closely monitored.

David B. Muhlhausen, an expert on criminal justice at the Heritage Foundation, accused Pfizer and other drug companies of “caving in to special interest groups.” He said that while the companies have a right to choose how their products are used, their efforts to curb sales for executions “are not actually in the public interest” because research shows, he believes, that the death penalty has a deterrent effect on crime.