Prescription drug abuse is the scourge of the nation and pills, like these Oxycontin tablets seized in Los Angeles, are scoring big bucks on the street.

NEW YORK (CNNMoney) -- Prescription drug abuse, now the fastest-growing drug problem in the country, has created a ballooning street market for highly-addictive pain relief, anxiety and depression drugs.

Given the money involved, it's no wonder.

Here's a sampling of the street prices for a single tablet of some commonly trafficked drugs, compared to their retail prices:

--Oxycontin: $50 to $80 on the street, vs. $6 when sold legally

--Oxycodone: $12 to $40 on the street, vs. $6 retail

--Hydrocodone: $5 to $20 vs. $1.50

--Percocet: $10 to $15 vs. $6

--Vicodin: $5 to $25 vs. $1.50

Those street prices were gleaned from the latest data put out by federal law enforcement agencies, and the retail prices were from pharmacychecker.com.

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As is typical in illegal drug sales, demand is driving the business.

Prescription drug abuse is spreading nationwide, but it is particularly rampant in cities like Los Angeles, Miami, Chicago and New York, federal officials say.

For decades, Marijuana was the gateway drug for first-time drug abusers in the United States. But two years ago, prescription drugs won that dubious distinction, according to Rusty Payne, a spokesman for the Drug Enforcement Administration.

"It's a significant shift in trend," Payne said.

In 2009, there were seven million Americans abusing prescription pain and anxiety drugs, up 13% from the prior year, according to the most recent data from DEA. The agency expects 2010 numbers to show another double-digit increase.

And there's big money in it for criminals. The trafficking in prescription drugs is close to becoming a billion-dollar industry, industry experts say.

In Los Angeles, 80mg Oxycontin is the most popular drug on the street with addicts. A single pill can fetch $80 or more, said Sergeant Stephen Opferman of the Los Angeles County Sheriff's Department.

"We are rounding up so much prescription [medication] off the street," Opferman said.

Prescription drugs leak out onto the street in a number of ways.

In some cases, thieves steal legitimate shipments. Or doctors write false prescriptions that dealers fill and then sell the contraband.

Medicare fraud is another route, according to Opferman, who has been battling illegal drug sales for more than 11 years.

Traffickers recruit Medicare beneficiaries who are willing to sell their monthly drug supplies for cash, Opferman said. The illegal activity costs Medicare billions of dollars a year, according to estimates from the federal Centers for Medicare & Medicaid Services.

But the most troubling trend among drug abusers in Los Angeles, Opferman said, is the growing number of young teens abuse prescription drugs.

"The kids think these drugs must be safer than heroin because their parents take them," he said. "They hold what they call 'skittles parties' where they try out sleeping pills, anti-anxiety pills and pain medicine."