Thailand has expressed interest in joining the Comprehensive and Progressive Agreement for Trans-Pacific Partnership (CPTPP), an 11-country plurilateral trade agreement whose original incarnation included the United States of America (USA). When the USA withdrew from this agreement, key intellectual property clauses relevant to pharmaceuticals were suspended. These could be reinstated should the USA decide to re-join. This study aimed to measure the impact of these suspended clauses by costing Thailand’s 2020 hepatitis C treatment program under four scenarios: 1) existing treatment regime, which does not use the currently recommended treatment regime and does not source the lowest price medicines, 2) treatment regime if Thailand joined the CPTPP and suspended clauses were reinstated, 3) treatment regime if Thailand utilised flexibilities in international law enabling access to the cheapest direct acting antivirals on the global market and 4) lowest-cost generic pan-genotypic regime on the global market. Joining the CPTPP would increase the cost of Thailand’s hepatitis C treatment program more than tenfold if suspended CPTPP clauses were reinstated and TRIPS flexibilities not fully utilised. Within the existing budget, the price and regime for scenario 4 would enable an additional 7,571 people to access hepatitis C treatment and avoid the need for genotype testing. Signing trade agreements such as the CPTPP that require stronger intellectual property protections could compromise Thailand’s hepatitis C program and other national treatment programs reliant on affordable generic medicines and prevent it from relying on its own pharmaceutical capabilities to manufacture medicines needed to sustain its treatment programs.