India, sometimes dubbed "pharmacy to the developing world", is facing pressure to change strict patent laws as it negotiates a trade deal with Europe.

Key points: India allows drug makers to legally manufacture and sell known drugs at cheap prices

India allows drug makers to legally manufacture and sell known drugs at cheap prices Free trade deal negotiations with Europe threaten its patent law

Free trade deal negotiations with Europe threaten its patent law India's patent system makes it extremely difficult to patent a formula

That would make it easier for drug companies to prevent the generic manufacture of medicines widely used to combat diseases like hepatitis and HIV, putting them out of reach for many.

When Australian Greg Jefferys found out he had hepatitis C two years ago, the cost of treatment rocked him more than the diagnosis.

"There was a new drug out that could cure it completely, but at the cost of $100,000," he said.

"Then I heard that the same drug in generic form was available in India, and it only cost $1,200.

"So I went to India and bought it, and now I'm cured."

The medicine was a generic version of a drug called Sovaldi, made by pharmaceutical company Gilead.

Gilead had sought an Indian patent, but its application was rejected.

India's patent system makes it extremely difficult to patent a formula if its active ingredients are already known.

The law is designed to prevent what is known as evergreening — where pharmaceutical companies vary an existing recipe then apply for a new patent.

For India's drug makers, their country's narrow interpretation of what constitutes an "innovation" means they can legally manufacture and sell known drugs, invariably for less than the original.

Free trade agreement threatening Indian laws: MSF

Leena Menghaney, a drug access campaigner with charity Medecins Sans Frontieres (MSF), said the millions of poorer people around the world depended on India's cheap pharmaceuticals.

"Fifteen million people today who are living with HIV are on Indian generic medicines," she said.

MSF is worried India could be forced into changing its rules under a free trade agreement being negotiated with Europe.

"These are provisions that are aimed at stopping competition from India," Ms Menghaney said.

"This is a very deadly game, because it means that in stopping competition from India, you're stopping them getting to patients who need them all across the world."

But trade observers doubt it will come to that.

India's Prime Minister Narendra Modi flew to Brussels for an EU-India summit earlier this week, but when he left, no deal appeared imminent.

The generic drug industry was worth $26 billion to India in 2014, and is forecast to double to around $50 billion by 2020.

India unlikely to allow deal to harm industry, expert says

South Asia University associate professor of trade law Dr Prabhash Ranjan said although India stood to gain in other areas from a trade deal, it was unlikely to give concessions that would harm the industry.

"If India has to do anything which goes beyond its existing IP [intellectual property] protection standards, which are WTO [World Trade Organisation] compatible, it will be very difficult to convince the domestic constituency that this is something which is in India's interest," Dr Ranjan said.

The medical tourism that the medicines attract is also hugely lucrative.

In China, the drug that saved Greg Jefferys is still awaiting approval, so Chinese hepatitis suffers come to India in their thousands for treatment.

But if India's patent law or customs rules that allow the drugs to be exported were ever changed, Mr Jefferys is unequivocal about the potential impact.

"People will die," he said.

"And not just a few. Hundreds of thousands of people will die."