WASHINGTON (CNN) - In a blow to the Republican leadership, the House of Representatives early Friday approved a controversial bill to allow Americans to import lower-cost prescription drugs from Canada and Europe, which proponents say could help curb escalating drug costs.

The bill passed 243-186, shortly before 3 a.m. ET.

The Bush administration and the leadership in the GOP-controlled Congress both oppose the bill, but some lawmakers feeling enormous pressure over rising drug costs have broken ranks to support it.

One of those members, Rep. Jo Ann Emerson, R-Mo., said if the bill fails, "Americans may remain under the thumb of the pharmaceutical industry for the foreseeable future."

"In America, breast cancer kills over 40,000 people, especially women, each year," she said on the House floor. "A bottle of Tamoxifen used to fight breast cancer costs $360 in the United States. It costs $60 in Germany. How long will American women who can't afford Tamoxifen continue to subsidize those in Europe who can?"

But opponents of the measure say it could lead to unregulated and unsafe drugs flooding into the United States and compromise free-market trade practices.

"This bill will only serve to undercut important safety protections and place foreign price controls on American businesses," said Rep. Michael Burgess, R-Texas. "We all want cheaper drugs, but not at any cost."

The House debated the measure deep into the night, before they approved the bill early Friday. The House is just one day away from adjourning for its August recess and is working overtime to finish a final handful of bills before leaving town.

The bill, written by another Republican, Rep. Gil Gutknecht of Minnesota, would allow consumers to import FDA-approved drugs from Canada and a handful of European countries. Drugs are often cheaper in those countries because governments negotiate lower prices with pharmaceutical companies.

While it is already legal to import prescription drugs, the bill would remove an existing requirement that the Secretary of Health and Human Services verify that the imported drugs are safe -- something secretaries in both the Clinton and Bush administrations have refused to do.

In a bid to boost support for the bill, Emerson tried to amend the language to allow only imports from Canada. But GOP leaders denied her request -- sticking to the letter of the agreement they struck with her last month when she agreed to cast the deciding affirmative vote for the Medicare reform bill in exchange for an up-or-down vote on this bill.

Upon its passage, the bill has become the official House position in its negotiations with the Senate over the Medicare reform bill. But lawmakers and aides on both sides of the issue said there is no assurance the drug import bill will survive that process.