People who have been stunned with Tasers may be unable to understand Miranda warnings - and more likely to waive their rights or even give false confessions - according to new research by a Drexel University professor.

The study, the first randomized controlled trial of the weapons outside of manufacturer Taser International, found the 50,000-volt shocks significantly impair brain function in the short term.

"People who have just recently been tased run the risk of talking to police without the benefits of counsel and not understanding the consequences," said Drexel criminology and justice studies Professor Robert Kane. It was published this month in the journal Criminology and Public Policy.

Kane said the study makes the case for a nationwide policy requiring police to wait an hour after using a Taser on a suspect before interrogating him.

Kane, 48, who came to Drexel from Arizona State University in 2012, began the work after he and his colleagues heard about lawyers in the Phoenix area seeking to suppress clients' confessions. Kanecollaborated with Arizona State University professors Michael White and Justin Ready on the research.

The lawyers in Arizona were arguing that their clients, having been stunned with Tasers, were unable to "knowingly, intelligently and voluntarily" waive their rights. That's the standard outlined in Miranda v. Arizona, the 1966 Supreme Court decision that held people must be advised of their constitutional rights to silence and to a lawyer before questioning.

With funding from the federal National Institute of Justice, the criminologists recruited 142 healthy individuals, mostly college students, who were willing to be Tasered, all in the interests of science.

Half were shocked; a subgroup underwent physical exertion before the shock, just as a suspect would be likely to have struggled with police.

Individuals who received the jolt performed worse on verbal learning tests and reported difficulty concentrating, elevated anxiety and feeling overwhelmed.

"People who get tased look a lot like 78-year-olds suffering from mild cognitive impairment and, in some cases, even patients with dementia," Kane said. On average, the effects subsided within an hour, though in some cases, it took up to a week.

Bradley Bridge, an assistant defender at the Defender Association of Philadelphia, said he'd be sharing the research with colleagues.

"This is new, and very troubling. It raises significant problems in terms of how the judicial system would deal with these issues," he said.

It could be grounds to argue that a defendant's waiver of rights was not knowing and voluntary - and that a confession must be thrown out. The question is likely to be litigated, he said.

A spokesman for the Philadelphia District Attorney's Office declined to comment on the potential impact of the research, referring the question to police.

Philadelphia police began issuing Tasers to front-line officers in 2007 in an effort to reduce the number of times officers resorted to gunfire. In 2010, the department invested heavily in the stun guns, bringing its arsenal from about 260 Tasers to 1,260.

City police have deployed Tasers more than 2,600 times since 2010, The Inquirer has reported. Department policy requires that anyone subjected to the device be transported to a medical facility for observation, but the policy makes no mention of any delay in interrogation.

A department spokeswoman said in an email that she was unaware of the new study by Kane and his co-authors.

Kane thinks the one-hour waiting period for questioning would be the best practice.

Police might argue that such a rule would prevent them from obtaining timely information, he said. But he dismissed that argument, noting the Supreme Court has already made exceptions to Miranda in cases where an immediate interrogation is necessary to resolve a threat to public safety.

Furthermore, Kane noted, his study might not even give the full picture of how Tasers impact mental function.

"We would expect 'typical' suspects - who may be drunk, high, or mentally ill and in crisis at the time of exposure - to experience even greater impairment," the study authors noted.

The study, which used five-second Taser exposures, also does not explore the effects on people who are Tased multiple times.

That's not uncommon, said David Rudovsky, a civil rights lawyer and University of Pennsylvania law professor.

"Tasers are often overused. People get re-tased, often, several times," he said.

Rudovsky said the study adds to concerns about the devices, which have been linked to physical injury and even deaths.

"The argument that an individual did not have his full mental capabilities at the time he gave the statement, that could certainly be a plausible claim in a suppression motion," he said.

Kane said, since the study was released last week, he's already received several phone calls from attorneys asking him to evaluate the circumstances under which their clients were tased and subsequently interrogated.

"This question will continue to come up as people learn more about this kind of research," he said.