Pfizer has taken a hard line against counterfeiters by adding RFID tags to the packaging of its Viagra tablets.

The tags aim to stiffen up the drug's security and allow wholesalers and pharmacists to check the authenticity of the drug.

However, products will not initially be tracked for the entire length of the supply chain as this would require the RFID technology to be deployed by individual pharmacies.

"The primary goal for adding the technology is to enhance patient safety," said Tom McPhillips, vice president of Pfizer's Trade Group.

"We want pharmacists who fill prescriptions for Pfizer medicines, and patients who use those medicines, to have increased confidence that they are receiving authentic products and not a potentially dangerous fake.

"We are creating additional barriers for criminals who might attempt to counterfeit our products."

Viagra is one of the most popular brands for counterfeiters and Pfizer has been actively improving product security.

Last year the company began a relationship with Microsoft to start suing spammers and websites that advertise fake Viagra. Initial probes resulted in two legal cases.