Lib Dem leader Sir Ed Davey said he is ready to vote against legalising assisted dying.
MPs are expected to debate a new bill on the controversial issue in the House of Commons next month.
The Liberal Democrat leader raised fears that the people could feel like “burdens” on their families.
He recalled caring for his mother and administering her morphine when she suffered from bone cancer.
Asked at a lunch with political journalists in Westminster today if he was ready to vote against the bill, Sir Ed said: “Yes.
“I’m going to listen to the debate and I think every single MP has listened very closely and been open-minded to it.
“It’s a free vote and I don’t know what all my colleagues will do, I’m sure some will vote for it.”
Sir Ed said he was “very minded to vote against it”, adding: “I genuinely worry that people could feel burdens on their loved ones and their family and without telling them say they agree to voluntary euthanasia. I think that is a deeply worrying position.
“I won’t go into all my personal experience but my mother had a very painful form of cancer and I used to administer morphine to her.
“I was by her bedside when she died and I can tell you that I don’t think she would have wanted anything different.
“The big thing I take from that is palliative care. We have got to be so much better on palliative care.
“I think if we did do that, it’s completely doable, I think many of the people who worry about this would have their worries reassured and there would be quite a strong consensus not to proceed down this road.
“I looked at what’s happened in Canada and they started quite narrow and it’s very quickly broadened to a lot of different groups of people. I think we should be very wary.”
Labour MP Kim Leadbeater’s private member’s bill would allow terminally ill adults, subject to safeguards and protections, to request and be provided with assistance to end their own lives.
The Government is officially neutral and MPs will have a free vote according to their conscience rather than along party lines.
