SAN DIEGO – A doctor who wrote prescriptions for nearly a million tablets of the powerful painkiller hydrocodone last year has been charged with seven others in what authorities described as a strike against a ring that smuggled prescription drugs to Mexico from the U.S., according to federal indictments obtained Friday.

The unusual operation brought a flood of yellow and blue hydrocodone tablets to Tijuana pharmacies, where American addicts snapped them up over the counter on jaunts across the border from San Diego, investigators said.

Authorities speculate it was easier for smugglers to unload large batches of pills at those loosely regulated pharmacies than to distribute them in small amounts through American street dealers.

It’s also profitable: A smuggler who buys a pill for about $2 in the United States can sell it to a Mexican pharmacy for about $3.50, and the American addict pays about $6 to bring it back home.

“We got Tijuana in the palm of our hand,” Jason Lewis, one of the people accused of smuggling, said in a wiretapped conversation, according to a search warrant affidavit filed in the case. “We’ve been doing this for years, bro.”

The risk of getting caught carrying drugs across the border into Mexico is minuscule. Motorists and pedestrians are almost never stopped for questioning, unlike the tough scrutiny they face when entering the United States.

No hydrocodone pills and only 90 oxycodone pills were seized from Mexico-bound travelers at U.S. border crossings in fiscal 2009, the year before the investigation began.

The 17-month investigation resulted in Tuesday’s arrest of Dr. Tyron Reece, 71, a general practitioner who runs a solo practice in the Los Angeles suburb of Inglewood. He did not immediately respond to a phone message Friday.

Reece wrote prescriptions last year for about 920,000 hydrocodone pills, which are commonly sold under the brand names Vicodin and Lortab, authorities said.

Smugglers strapped pills to their bodies or hid them in engine compartments before crossing the border. Their favorite checkpoint was San Ysidro, the nation’s busiest crossing, which connects San Diego and Tijuana. They usually crossed at night.

By law, Mexican border pharmacies must get prescriptions from Mexican doctors for powerful painkillers and psychotropic drugs. But it’s easy to find ones that will break the law around Tijuana’s main tourist drag, Avenida Revolucion.

On a recent Saturday, a man behind the counter of a tiny pharmacy near the strip offered hydrocodone for $10 a pop, oxycodone pills for $15 each and 90-tablet bottles of Valium for $130. He spoke fluent English.

Hydrocodone, nearly as powerful as morphine, caused 2,499 deaths in the United States from 1998 to 2002, the most recent data analyzed by the Drug Enforcement Administration. The DEA says 130 million prescriptions were written in 2006, up nearly 50 percent over six years.