Mr Key said if he was terminally ill and suffering, "if they just effectively wanted to turn off the switch and legalise that by legalising euthanasia, I'd want that".
"I look at a situation where I think there's a lot of euthanasia that effectively happens in our hospitals."
Mr Key's comments on euthanasia could almost be written-off as "outdated", Dr Thurlow said.
"It's sort of a traditional view of end of life. That word 'suffering' is less common than it used to be 20 years ago.
"A lot of the time people will turn around and say, 'I can't believe I was considering that [physician-assisted suicide]'."
New Zealand's national palliative care body has also hit-out at Mr Key, labelling him a "lay person" whose observations around euthanasia demonstrated an ignorance of end-of-life care practices.
"Euthanasia is a doctor deliberately ending the life of a patient and that's illegal and it's unethical, so that's not happening in New Zealand hospitals," said Dr Sinead Donnelly, chair of the Australian and New Zealand Society of Palliative Medicine Aotearoa (ANZSPM).
"[Mr Key] may think ... when you give morphine to someone who's dying to relieve their pain that [it] somehow hastens their death. But it doesn't. If someone is dying and they are in pain, we are trained to know how to use small doses of morphine and increase them if necessary to relieve that person's pain."
A yet-to-be-drawn private member's bill by Labour MP Maryan Street would legalise medically-assisted death.
Mr Key has said he is undecided on the bill. But he voted in favour of the failed 2003 Death with Dignity bill, proposed by former NZ First MP Peter Brown.
Dr Donnelly said Mr Key's comments threatened palliative care services in New Zealand, and could be harmful for families and patients considering end-of-life treatment options.
"They may be then fearful of what we might do."
Hospice NZ services treated nearly 14,000 people nationwide last year. Its teams made more than 155,000 home visits and volunteers contributed nearly 600,000 hours of community work.