Prime Minister John Key appears to be softening up the public for some unpopular concessions under the Trans Pacific Trade Partnership being negotiated at present.

He told the US-NZ Partnership Forum in Christchurch he knew the prospect of trade liberalisation had made some sectors in the United States anxious. But New Zealand would also face requests, including from the US, which it had not faced in previous free trade agreements.

"When facing such challenges it is important that we all remind ourselves of the overall collective benefits in getting TPP right, of which there are many."

Asked later if he could abandon Pharmac, which bulk-buys generic medicines, he said all parties would need to confront challenges.

"But what we will do is once we can get a clear sense of what is required to make the deal work, then we will go back and analyse the benefits of that.

"In the end, we're not going to sign any deal unless we believe it has a net benefit to New Zealand."

Mr Key said there could be some issues around intellectual property.