The inner workings of a fraudulent Bronx clinic have been exposed after a federal investigation found that the medical chain sold up to $550 million worth of oxycodone pills to thousands of people.

Astramed Physicians has reportedly filled over 30,000 prescriptions for potent opiates since 2011, in what the Drug Enforcement Administration has called “the largest pill mill in the Northeast.” The clinics run by Dr. Kevin Lowe allegedly charged $300 for each doctor visit, though each session lasted only a few minutes and did not involve a physical evaluation.

One prescription could be up to $6,000 in New York, and $18,000 out of state. According to investigators, some 5.5 million tablets were ordered.

According to the NBC News investigation that initially uncovered the clinic’s dealings in 2012, there were several “corrupt, Board certified, state licensed doctors who, in exchange for cash, were willing to write medically unnecessary prescriptions for large quantities of oxycodone.”

A patient who went to Astramed was prescribed excessive amounts of oxycodone after a brief examination at the clinic. The 37-year-old patient eventually became addicted. “It’s a pill mill — this is the type of practice you can go to, no questions asked,” the patient, who asked to remain anonymous, told NBC News. “And now I’m addicted to something that people prescribe to you.”

Some 25 people have been charged with playing roles in the enormous drug scheme, including doctors, office workers, and “bouncers” who actually intimidated patients and ordered them not to talk to police. “To the extent that you’re able to shut down a major supplier to the black market, you are going to save lives,” Special Narcotics Prosecutor Bridget Brennan told NBC News. “Over 4,200 individuals received prescriptions at this clinic in the Bronx.”

Though the Bronx Astramed Physicians scheme was probably one of the largest, it certainly isn’t the only one to falsify prescriptions. In 2013, a Miami clinic found a way to achieve its own performance-enhancing drug (PED) scandal. The clinic was the source of PEDs for over 30 Major League Baseball players, including Alex Rodriguez and Melky Cabrera. Anthony Bosch, an operator of several wellness clinics, maneuvered several prescription forms containing forged signatures as well as stamped names of legitimate physicians who had been deceived into signing. The ESPN report notes:

Anthony Bosch, the self-described biochemist who operated a series of wellness clinics, used prescription forms that contained forged signatures, stamped with the names and license numbers of legitimate physicians who apparently were unaware of the scheme, sources and documents indicate. Those drugs were prescribed to Bosch’s friends and associates and then delivered to professional athletes in order to avoid a paper trail, sources said.

Another prescription drug scheme based in Dallas was busted this year as well, involving a pharmacist and four others who filled out fake prescriptions in order to illegally distribute controlled substances. According to the Dallas News, those involved in the scheme found "fake patients" in homeless shelters and elsewhere, who were given the prescriptions and pills, and then handed them over to drug dealers who sold them on the street for a high profit.

According to the Center for Problem-Oriented Policing, a survey carried out in 2009 found that between 28 and 58 percent of police agencies in the U.S. reported "street-gang involvement in pharmaceutical drug distribution." Illegal prescription drug activity is often a more ornate and robust scheme than traditional street drug trafficking; U.S. Attorney Preet Bharara described the profitable Bronx clinic as something that "would make harded illegal drug traffickers envious."