The world-renowned religious leader, writing in a Sunday newspaper, said he reveres "the sanctity of life - but not at any cost".
His comments come after the former Archbishop of Canterbury, Lord Carey, said he had changed his mind on the issue of assisted dying, after considering cases like that of locked-in syndrome sufferer Tony Nicklinson and "the reality of needless suffering".
Proposals to legalise assisted suicide in Scotland were lodged by the late Margo MacDonald in November. South of the border, former Labour Lord Chancellor, Lord Falconer's Bill, which proposes allowing doctors to prescribe a lethal dose to terminally ill patients judged to have less than six months to live, will come before the House of Lords for a second reading on Friday.
Retired archbishop Mr Tutu, 82, while recognising the sensitive nature of the subject, said there needs to be a greater focus on the treatment and preservation of newborns and the young.
"Money should be spent on those that are at the beginning or in full flow of their life. These are my personal opinions and not of my church," he wrote.
Strongly condemning the treatment of Nelson Mandela in his later years, Mr Tutu said it was "an affront to Madiba's dignity" to force him to be part of a television appearance with other political leaders as he neared the end of his life.
He notes that the Lords Bill will be debated on the first anniversary of Mr Mandela's death.