Patients are being put at risk as counterfeiters target the NHS supply chain with fake drugs, regulators say.
Statins differ in price
The Medicines and Healthcare Products Regulatory Agency (MHRA) warned it is investigating twice as many counterfeit cases as it was five years ago.
The growth in fake drugs is said to be driven by huge demand for lifestyle medicines such as Viagra.
Counterfeits can be weaker doses of established drugs or medicines produced with substances such as paint.
The MHRA said the illegal trade carries lower risks and higher profits than smuggling hard drugs, and producers of fake drugs are now said to be targeting the pharmaceutical wholesalers who supply the NHS.
When EU customs officers seized a counterfeit heart drug last year it was found to contain brick dust coated with yellow paint and was covered with furniture polish to give it a glossy finish.
The MHRA said instead of selling small quantities of fake drugs to individuals over the internet - the traditional target - the counterfeiters are switching their attention to pharmaceutical wholesalers who supply the NHS.
However, the drugs which have been found to have entered the NHS supply chain to date have only included different doses of active ingredients and have not harmed patients.
The regulator said five incidents have been detected in the past two years in which counterfeit medicines have reached patients through high-street pharmacies after the NHS supply chain was penetrated. Prior to that there had been no incidents since 1994.
Another 25 cases are currently being investigated.
Naeem Ahmed, the head of intelligence at the MHRA, said: "If you trade over the internet the risk of detection is low but you only sell a pack here and a pack there.
"If you penetrate the supply chain, there is a higher risk but you can make a lot of money.
"From the source countries such as China and India it is possible to purchase the active ingredients incredibly cheaply.
"In the past couple of years the counterfeiters have become more confident. They have realised the profits to be made."
Mr Ahmed added: "When these people penetrate the NHS supply system that is a direct risk to the public.
"If someone chooses to buy their drugs over the internet then it is a case of buyer beware. We try to discourage that.
"But if a patient has gone through the NHS and been prescribed drugs, the last thing we want is for them to be put at risk."
The MHRA is planning to publish its anti-counterfeiting strategy, developed over the past three years, early in the new year.
It will set out priorities for customs officers and other enforcement agencies, including a list of the most commonly counterfeited drugs and the commonest routes used into Britain.