PHOENIX -- Methadone-related deaths are becoming more common in the U.S., police said.

In fact, the number of deaths increased 390 percent between 1999 and 2004, experts said.

In the Valley, nearly 80 people died of methadone overdoses in 2006, compared with 58 deaths in 2004.

Methadone, once primarily a drug used to treat heroin addicts, is increasingly being prescribed because it is inexpensive and effective for pain, doctors said. Though addicts are typically given 40-milligram tablets, the average patient receives much less.

Nevertheless, at least one doctor at the Pain Center of Arizona believes the drug is overkill for most pain.

"One milligram of methadone is equal to about one Vicodin tablet," Dr. Jeff Bucholz said. "That's a pretty rare patient that's going to need medication that strong."

Some of the people receiving it -- whether they are addicts or simply in pain -- now sell it on the black market, said James Molesa from the Drug Enforcement Administration.

Methadone normally costs $50 to $100 per pill on the black market, he said.

"It's a huge profit margin," Molesa said.

In 2006, the FDA put a black box warning on packages of methadone -- the strongest possible warning label.

Nevertheless, police said they don't think the trend toward recreational use will slow down.

"I think we're going to see more of it," said Flagstaff police Sgt. Tom Boughner.