David Cameron has warned there are "dangers" in the right to die proposals MPs are set to vote on for the first time in almost 20 years.
The Prime Minister said he did not see a case for introducing the Assisted Dying Bill and warned against an "expansion of euthanasia".
Proposed new laws passed an initial vote in the House of Lords last year but failed to make further progress.
In the landmark Commons debate, MPs will have a free vote on the issue, which will break across party lines.
Speaking in Leeds, Mr Cameron, said: "This a conscience issue, there won't be any party whips on this."
He added: "The decision I've come to is I don't see a case for this measure. I don't want to see an expansion of euthanasia in our country. I think there are dangers and so I don't support it.
"But, I do recognise it's time for a debate and it's right for the House of Commons to be debating this."
He added: "If the Bill makes more progress there will be further opportunities to scrutinise this legislation, ask difficult questions about it and to examine the whole subject, which I think is what the nation wants us to do."
"I don't think I'll be supporting it," he added.