The National Health Security Office said it would propose the health ministry issue so-called compulsory licenses on the drugs, unless the government reaches a deal with global pharmaceutical firms to lower prices.
The drugs currently cost Thai patients as much as 100,000 baht (2,920 dollars) per month per person, said Sanguan Nitayarumphong, head of the office that runs a free treatment programme for the poor.
The drugs being targeted include Novartis' Imanitib.
"We might have to impose compulsory licenses of these drugs if negotiations with the patent holders fail," said Sanguan, adding talks have yet to begin.
"The drugs are so expensive for Thai patients. The generic version would provide them greater chance to access the drugs at much cheaper prices."
The drugs that could be affected include Imanitib and Letrozole from Novartis; Docetaxel from Sanofi-Aventis; and Erlotinib from Genentech, he said.
Sanguan said the drugs were essential for Thailand because cancer is a leading cause of death in the kingdom.
Thailand has locked horns with Western pharmaceutical giants by issuing compulsory licenses, which temporarily suspend patent protections, for expensive medications.
The government has so far approved compulsory licenses for Plavix and two key AIDS drugs -- Kaletra and Efavirenz -- and has threatened to expand its generic programs to include cancer drugs.
It has already begun importing cheaper versions from India, a major source of generic drugs.
Plavix, which can help reduce the risks of heart attack or stroke, is sold by French-based Sanofi-Aventis and its US partner, Bristol Myers-Squibb.