training these doctors must go through are intended to make sure they meet the US's high quality standards, which US medical industry groups say are unmatched elsewhere in the world.
Some development experts are also loath to make it too easy for foreign doctors to practise here because of the risk of a "brain drain" abroad.
But many foreign physicians and their advocates argue that the process is unnecessarily restrictive and time-consuming, particularly since America's need for doctors will expand sharply in a few short months under President Barack Obama's health care law.
The US already faces a shortage of physicians in many parts of the country, especially in specialties where foreign-trained physicians are most likely to practice, like primary care.
Immigrant advocates and some economists point out that the medical labour force could be ramped up much faster if the country tapped the underused skills of the foreign-trained physicians who are already here but are not allowed to practise.
Canada, by contrast, has made efforts to recognise more high-quality training programs done abroad.
"It doesn't cost the taxpayers a penny because these doctors come fully trained," said Nyapati Raghu Rao, the Indian-born past chairman of the American Medical Association's international medical graduates governing council.
"It is doubtful that the US can respond to the massive shortages without the participation of international medical graduates. But we're basically ignoring them in this discussion and I don't know why that is."
For years the US has been training too few doctors to meet its own needs, in part because of industry-set limits on the number of medical school slots available.
Today about 1 in 4 physicians practising in the US were trained abroad, a figure that includes a substantial number of US citizens who could not get into medical school at home and studied abroad.
But immigrant doctors, no matter how experienced and well trained, must run a long, costly and confusing gauntlet before they can actually practise here.
The process usually starts with an application to a private nonprofit organization that verifies medical school transcripts and diplomas. Among other requirements, foreign doctors must prove they speak English; pass three separate steps of the US Medical Licensing Examination; get US recommendation letters, usually obtained after volunteering or working in a hospital, clinic or research organization; and be permanent residents.
The biggest challenge is that an immigrant physician must win one of the coveted slots in America's medical residency system, the step that seems to be the tightest bottleneck.
That residency, which typically involves grueling 80-hour workweeks, is required even if a doctor did his residency overseas. The only exception is for doctors who did their residencies in Canada.
The whole process can consume upward of a decade — for those lucky few who make it through.
The counter-argument for making it easier for foreign physicians to practise in the US is that doing so will draw more physicians from poor countries. These places often have paid for their doctors' medical training with public funds.
"We need to wean ourselves from our extraordinary dependence on importing doctors from the developing world," said Fitzhugh Mullan, a professor of medicine and health policy at George Washington University in Washington, DC.
About 1 in 10 doctors trained in India have left that country, he found in a 2005 study, and the figure is close to 1 in 3 for Ghana.
No one knows exactly how many immigrant doctors are in the US and not practising, but some other data points provide a clue. Each year the Educational Commission for Foreign Medical Graduates, a private nonprofit, clears about 8,000 immigrant doctors to apply for the national residency match system. Normally about 3,000 of them successfully match to a residency slot, mostly filling less desired residencies in community hospitals, unpopular locations and in less lucrative specialties like primary care.
Over the last five years, an average of 42.1% of foreign-trained immigrant physicians who applied for residencies through the national match system succeeded. That compares to an average match rate of 93.9% for seniors at America's mainstream medical schools.
The residency match rate for immigrants is likely to fall even lower in coming years. That is because the number of accredited US medical schools, and therefore US-trained medical students, has increased substantially in the last decade, while the number of residency slots has barely budged since Congress effectively froze residency funding in 1997.