The Prime Minister has reiterated the Government's position on Pharmac and is not ruling out possible changes to the way it operates under free trade talks.
Texts from the Trans Pacific Partnership negotiations were leaked at the weekend.
Opponents say the texts confirm the United States is out to destroy New Zealand's drug buying agency.
Pharmac buys subsidised drugs for the public health sector and can bargain prices down.
Auckland University law professor Jane Kelsey, who is a critic of free trade, says the leaked papers confirm the agency is very much in the gun.
John Key says the Government understands the importance and success of Pharmac and it would have to be a very good deal before there was any trade-off.
The Green Party says Pharmac saves New Zealanders hundreds of millions of dollars and the Government should be defending it more staunchly.