Eleven doctors and a GSK regional manager have been charged over alleged corruption between 2010 and 2012.
A former sales rep said doctors were paid to promote GSK's asthma drug Seretide.
The company said one employee had been disciplined and it was co-operating with investigations.
If the allegations are proved, GSK may have violated both the UK Bribery Act and the US Foreign Corrupt Practices Act. It is illegal for companies based in either country to bribe government employees abroad.
A former sales rep for GSK in the Polish region of Lodz, Jarek Wisniewski, said: "There is a simple equation," he said. "We pay doctors, they give us prescriptions. We don't pay doctors, we don't see prescriptions for our drugs.
"We cannot go to doctors and say to them, 'I need 20 more prescriptions'. So we prepare an agreement for them to give a talk to patients, we pay £100, but we expect more than 100 prescriptions for this drug.
"It's a bribe," Mr Wisniewski said, confirming that although on paper the payments were for educational services, the doctors understood very clearly that they must produce a certain number of prescriptions in return.
The Lodz public prosecutor found evidence in documents given to doctors by GSK to support claims of corrupt payments in more than a dozen different health centres where there was no evidence "patient education" had taken place.
Spokesman Krzysztof Kopania said: "We have evidence that in more than a dozen cases it was a camouflaged form of a bribe.
"In return for the financial gains the doctors would favour the product proposed by the pharmaceutical company and they prescribed that medicine."
One doctor has already admitted guilt, been fined and given a suspended sentence. He said he accepted £100 for a single lecture he never gave, but only under pressure from a GSK drugs rep.
He told Panorama: "They kept tempting, and I am just a man." (Más)
"GSK is now investigating claims that bribes were paid to doctors in Poland, Iraq, Jordan and Lebanon, following a much larger case of alleged bribery in China."
Será "cultura de empresa"?
Es que tanto y tanto...