NASHVILLE, Tenn. -- Specially trained Nashville officers will be allowed to use Tasers after a national study supporting their use by law enforcement, the police department said Thursday.

Video: Metro Officers To Be Armed With Tasers

Police Chief Ronal Serpas suspended use of the devices in 2005 while the scientific and medical communities studied their effect on people experiencing excited delirium, a condition associated with drug use.

Doctors and police said they wonder if there's a medical link between delirium and Taser use, but some doctors said they feel the risk is worth it because Tasers protect police and sometimes other people.

Serpas said the department has ordered 120 new Tasers for each certified officer and cited more medical evidence that supports the effectiveness of Tasers in law enforcement.

"The medical reports have been showing that there's no evidence that people are being long-term (injured), but, as with everything in our business, if there is a change in that literature or there is a change in that experience, we’ll obviously change right away," Serpas said.

Tasers deliver a 50,000-volt jolt through two barbed darts that can penetrate clothing. The company has warned departments to limit their use on suspects who show signs of the condition.

Findings from a recent Justice Department-sponsored study on the devices support their use, although the study said Tasers are not risk-free.

A recent article in the magazine Emergency Medicine News said there is no credible proof that the Taser induces cardiac arrest when used correctly by law enforcement officials.

Amnesty International said in a report last year that 156 people had died in the U.S. after being shocked by police stun guns, including 61 the year before. The report said the stuns can be fatal in certain circumstances, most often when the victim is using illegal drugs.

In Knoxville, Tenn., last year, authorities determined a man shocked by a Taser during an encounter with police died from cocaine in his bloodstream, not the three electric jolts he received from the stun gun.

A similar condition was cited in the 2005 death of a Nashville man after police shocked him 19 times with a Taser when they responded to the victim running around naked outside a nightclub.

In the 2005 death, police said Patrick Lee was running from officers in the parking lot of Mercy Lounge when he was Tasered. Lee’s family has since filed a lawsuit against Metro. The judge in the case has placed a gag order on everyone involved.

In addition, Serpas said a department committee has developed a "best practices" guide for officers who encounter individuals exhibiting signs of excited delirium.

Serpas said new guidelines for Taser use will allow officers to call for help when dealing with people who might be over stimulated because of drugs.

"The medical professionals here in Nashville will issue -- or administer I should say -- a drug that has a tranquilizing-type effect to calm them down so that we can get them to medical treatment," he said.

Supervisors and all officers will have to start over with eight hours of training before they're qualified to use Tasers. The certification process begins on Monday.