A naked man on drugs died in Wisconsin this weekend, after police used a Taser stun gun to subdue him. A student died at the University of Cincinnati after balling his fists and getting tasered by police. A man high on drugs in Manassas, Va., also died this weekend after police tasered him as he escaped, partially handcuffed, after punching an officer and a firefighter.

All three deaths are being investigated. One of the departments, the University of Cincinnati Police Department, has suspended the use of Tasers by its officers.

About 15,000 US police departments, including 29 of the nation's 33 largest cities, use a total of 260,000 Tasers. The devices have been the objects of controversy since first being deployed broadly in the 1990s. Some describe them as an alternative to the nightstick that reduces officer injuries and saves lives. Others see the stun guns as instruments of torture whose growing use make them a symbol of reckless policing.

In some cases, the Tasers are only tangentially related or unrelated to the actual cause of death, and that may be the case in the three incidents from this weekend. But recent studies have shown that the weapons can have an outsized impact on people with health problems or who are very high on drugs and in a state of "excited delirium."

Tasers contributed to some 351 US deaths between 2001 and 2008, says Amnesty International, which adds that 90 percent of those tasered were unarmed at the time they were electrocuted. The website Truth Not Tasers claims that 39 people have died in relation to "conducted energy devices (CEDs)" this year in the United States, an average of five per month.

On the other hand, 99.7 percent of people who are tasered suffer no serious injuries, according to a May report from the National Institute of Justice. "The risk of human death due directly or primarily to the electrical effects of CED application has not been conclusively demonstrated," says the report.

A growing number of police departments have begun to limit Taser use, imposing stricter policies for use or even taking the instruments out of officers' hands. Memphis, San Francisco, and Las Vegas police departments have all opted out of Taser use recently, amid growing questions about the level of threat necessary to justify electrocuting someone with 50,000 volts delivered through barbed bolts.

"Because of the criticism and the deaths, there's been a lot of people backing off of Tasers," says Samuel Walker, a professor emeritus at the University of Nebraska at Omaha, who studies police accountability. "The fact is, a lot of departments are taking some very positive, proactive steps to ensure accountability, and controlling Tasers is one of part of doing that," he says. But in other departments, he adds, "they're using it much too broadly and recklessly, where it isn't appropriate."

The current Taser debate hinges on when, not if, the stun guns should be used. Few disagree with the use of Tasers as an alternative to deadly force, but in some departments, officers can employ Tasers when someone is simply refusing to obey an order.

Tasers are often most used when police officers are dealing with unruly people who themselves are unarmed, but whose failure to comply with police instructions make officers to feel threatened. Most departments use the "billy club policy," which holds that Tasers are appropriate in any situation where an officer would otherwise pull and be ready to use a billy club, or night stick, which tends to lead to more serious injuries than a Taser.

Taser opponents point to the public outrage over the tasering of a fan at a Philadelphia Phillies baseball game, and various lawsuits documenting officers using Tasers on subdued, non-aggressive, or even handcuffed people. Tasers "can be used too much and too often," the National Institute of Justice found in its May report.

At the same time, some law enforcement officials have pushed back against setting higher standards for Taser use.

"Police chiefs are saying, don't write the standards so that it's going to take away decision-making ... when I write my own policies," says John Gnagey, executive director of the National Tactical Officers Association, in Doylestown, Pa. "The argument that Tasers should only be used when the use of deadly force is authorized is asinine."

After releasing an advisory in 2009 urging police not to shoot suspects in the chest, Taser International is now marketing the old version of its gun, which allows for only a five second blast of current before officers have to make the decision to hit the suspect again. A newer version of the gun allowed officers to apply continuous current, which the NIJ said in a separate May report has been associated with deaths.

In all three cases from this weekend, the victims were acting erratically and, in at least one, in Manassas, Va., the man had already physically assaulted a police officer. But whether the occasions rose to a level where officers would have used deadly force is far from clear. None of the three men were armed.

In Kaukauna, Wisc., police responded to a report of a naked, out-of-control man running across a city bridge. When police reached him, the man appeared to be in the throes of a drug overdose, claiming he was covered in snakes. When he refused to comply with officers, a Taser was used to knock him down.

At the University of Cincinnati, a recent high school graduate, at the university for college-preparatory summer classes, was approaching the police with an "altered mental status" and balled fists when he was brought down with a Taser. The University of Cincinnati Police Department has suspended the use of Tasers as it investigates the case. One newspaper account said the officer who fired the Taser was "very distraught" by the young man's death.

Some police departments, including Kansas City, Seattle, and Madison, Wisc., have begun publishing their Taser policies on their public websites, in an effort to increase transparency and respond to public concerns. None of the three police departments involved in this weekend's incidents publish their policies on Taser use, with one – Prince William County – citing "tactical concerns." Calls to the other two departments were not returned by the time this story was posted.

"This is a very important point of accountability that goes beyond Tasers, a form of openness and transparency," says Professor Walker.

Some battles over Tasers have played out in the courts.

"Tasers and stun guns fall into the category of non-lethal force; non-lethal, however, is not synonymous with non-excessive force," ruled the Ninth Circuit Court of Appeals in 2009. "All force – lethal or non-lethal – must be justified by the need for the specific level of force employed."

In July, a North Carolina jury returned a $10 million verdict against Taser International, the maker of the stun guns, for the 2008 death of a 17-year-old in Charlotte, N.C., ruling that company failed to provide police with adequate warnings or instruction. Taser International plans an appeal.

The day of the North Carolina verdict, another Charlotte man died in a Taser-related incident, prompting that city's police department – considered one of the most professional in the nation – to impose a 45-day suspension on the use of the weapons, to review their polices.

"My personal opinion is that when departments become restrictive and take away a tool, it's generally because they're afraid of some sort of public pressure coming from a certain segment of society," says Mr. Gnagey. When public pressure does succeed in restricting or banning Tasers, he adds, "Later on, when things die down, we'll just quietly introduce it back into the population."