Costly drugs that boost red blood cells are being routinely misused in cancer patients, raising concerns about side effects and wasted resources, researchers say.

A quarter of the time, they found patients got the so-called erythropoiesis-stimulating agents (ESAs) for no more than a week, which is too short to do much good.

"These are very expensive drugs and there are a fair number of side effects," said Dr. Jason Wright of Columbia University Medical Center in New York, whose findings were published in the Journal of Clinical Oncology.

According to recent estimates, Medicare spends more than $1 billion dollars annually on ESAs, which include brand-name products such as Amgen's Epogen and Roche's NeoRecormon.

The medications are approved for cancer patients who are getting chemotherapy, and the recommended treatment is between two and 14 weeks.

Outside of that, the benefits are murky and could be outweighed by side effects. Those include blood clots and heart problems, and in some cases the drugs might even fuel tumor growth.

"Over the last five years, we have been seeing many side effects that weren't seen in the early clinical trials," Wright explained, adding that the U.S. Food and Drug Administration issued their strongest warning about ESAs in 2007.

Many other drugs have turned out to hold nasty surprises, not least when doctors prescribe them outside of their approved indication -- so-called off-label use.

On Wednesday, for instance, one research team found an antipsychotic given to tens of thousands of U.S. veterans with post-traumatic stress disorder has no benefit, but causes weight gain and sleepiness.

Wright's team used data on 21,000 Medicare beneficiaries with common cancers who'd been given an ESA, such as Amgen's Epogen, between 1995 and 2005.

As it turned out, 24 percent of the patients got the drugs for a week or less.

"You're subjecting patients to potential toxicity for very little clinical benefit, so it is wasted resources," Wright told Reuters Health.

What's more, eight percent of the Medicare beneficiaries received the medicine for more than 14 weeks, while 14 percent were getting the drugs when they weren't on chemotherapy.

"What we are concerned about is that physicians don't always realize the correct way to prescribe these drugs," Wright said.

It's hard to know exactly how to explain the results. Doctors might be stopping the medicines early because their patients don't tolerate them well.

But when it comes to off-label and prolonged use, there is another, more worrisome possibility.

Indeed, previous research shows doctors prescribe more ESAs when they are working in a fee-for-service system. Wright's team also found private practice doctors were more likely to prescribe the drugs for prolonged periods than others, while they were less likely to use them for less than a week.

"Patients need to be aware of the drug that their doctors are giving them," said Wright.

Dr. Thomas J. George, who was not involved in the study, said the enthusiasm for ESAs has dampened somewhat after the side effects surfaced.

"The really important question now is whether it is still being used routinely, because that would be a real public health concern," said George, a cancer researcher at the University of Florida.

In the meantime, he told Reuters Health, "there needs to be a fairly rigorous educational program that accompanies the use of these medications so doctors know who is going to benefit."