In more than 30 years of negotiating trade deals, "dairy is always the last or one of the last few issues to be resolved because it has been so distorted for so long," he said.
Without improved dairy access, the New Zealand government will face deep criticism at home, while even a small increase in the current five year life for drug patents would increase costs for the government's drug-buying agency, Pharmac, which controls the purchase of pharmaceuticals subsidised by the public health system.
Pharmac achieves major savings for taxpayers by waiting for new treatments to fall out of their patent periods and be manufactured more cheaply as generics by competing drug makers.
Pharmaceutical patents tend to run five years, but pharmaceutical firms - many of them US-headquartered - have been pushing for an extension to 12 years, with negotiations understood to have centred on pulling that back to perhaps seven years.
Asked whether New Zealand had ever considered abandoning the TPP talks because of the difficulty of getting a reasonable deal on dairy products, Groser said he was "not emotionally in the space of wanting to leave the party", given that New Zealand had initiated the TPP in the first place.
"We will not be pushed out of this agreement," he said.