The new bioethics instruction was approved by Pope Benedict XVI
The Vatican has updated its opposition to embryonic stem-cell research, in-vitro fertilisation and human cloning in a sweeping new document.
The Catholic Church also said the morning-after pill and drugs preventing the implantation of the embryo during pregnancy were "gravely immoral".
The rulings came in a Vatican document released to respond to scientific advances made in the past two decades.
Catholic doctrine says life begins at conception and must be respected.
Dignitas Personae (The Dignity of a Person), an Instruction of Certain Bioethical Questions, was issued by the Vatican's doctrinal body, the Congregation for the Doctrine of the Faith, and approved by Pope Benedict XVI.
The 32-page document condemned new forms of birth control that "fall within the sin of abortion".
It also reiterated Catholic teaching that responsible human procreation should take place through an act of reciprocal love between a married couple.
It said human life deserved respect "from the very first stages of its existence and can never be reduced merely to a group of cells".
The instruction updated the Vatican's 1987 instruction, Donum Vitae (The Gift of Life), which enshrined the dignity of the human embryo.
But while the updated document denounced embryonic stem-cell research - which it noted invariably resulted in the destruction of the embryo - it said adult stem cell research was allowed, as the subject was unharmed by the process.