An old treatment is making a comeback in the battle against alcoholism.

Scientists have made a simple change in a drug used to curb cravings, and it's making a big difference in its success.

But there's a catch with this new version: early research suggests it only works in men.

It's an injectable version of the drug Naltrexone, which works by blocking brain chemicals that trigger the euphoria from drugs and alcohol.

An older, version of Naltrexone has shown some success in curbing cravings in alcoholics.

But it's a pill and only works if patients take it every day.

"Several of the studies showed it wasn't as strong of an effect, most of the patients stopped taking the medication after a couple of months," said Harold Urschel, psychiatrist at the Southwestern Medical Center.

The Naltrexone injection may help overcome that hurdle, because its effects last an entire month.

"I had already given up, then this came along and I'm telling you, this has given me so much confidence," said Kenneth McKnight, a recovering alcoholic.

McKnight said the shot is helping him break a nearly 20-year drinking habit.

"And it really works, no way to explain it to you. The cravings aren't there, that's the whole deal," said McKnight.

A study of more than 600 men and women found the injection curbed heavy drinking in men by nearly 50 percent compared to a placebo.

Unlike the pill version, the Naltrexone shot had no effect on women, which puzzles researchers.

They are hoping a large national study now under way will provide some answers.

"These meds will not cure you. They make it easier for you to learn and understand the new coping skills you have to develop to stay sober," said Urschel.

They are skills that are helping McKnight get his life back.

"I couldn't even start to tell you what alcohol and drugs have cost me - I've paid a lot for them," McKnight said.

The Naltrexone injection could be up for Food and Drug Administration review as early as next year.

The drug will be marketed under the name Vivitrex and is also being tested as a treatment for drug addiction.

The only real side effect of the Naltrexone injection is pain at the injection site.

It's estimated that up to 18 million people in the United States suffer from alcohol dependence or abuse.

Alcohol abuse is the cause of more than 100,000 deaths in America each year and costs americans a total of $184.6 billion annually, according to the National Institute On Alcohol Abuse and Alcoholism and the National Institute On Drug Abuse.