Access to affordable medicines could be under threat in Australia if the United States gets its way in secretive negotiations over a massive trade deal involving 12 Pacific-region countries, academics have warned.

If Australian negotiators give the US what it wants in these negotiations they will also put at risk the financial sustainability of Australia's Pharmaceutical Benefits Scheme, they say.

Pharmaceutical monopoly protections cost the Australian health system hundreds of millions of dollars each year, according to Dr Deborah Gleeson. Credit:Louie Douvis

Dr Deborah Gleeson, from Melbourne's La Trobe University, has warned in the Medical Journal of Australia that pharmaceutical monopoly protections already cost the Australian health system hundreds of millions of dollars a year, and new US ambitions for intellectual property protections would "expand and entrench" those monopolies, making it even costlier.

Ms Gleeson says leaked drafts of part of the secretive trade deal, the so-called Trans-Pacific Partnership Agreement (TPPA), also show that the government will find it harder to pursue patent reform in the future if it agrees to US demands.