There is no definitive teaching of the Church, it does not exist. What does organ donation mean? Does it mean you are dead? If the body is dead, it cannot be a living organism.
This so-called brain death is an artificial definition of a non-functioning brain, and there are cases where these so-called brain-dead people begin to wake up and start to live. With this, there is a lot of abuse and manipulation with organ donations. Brain-dead people still have a soul in their bodies, and it is not separated.
This would be a very confusing situation, and the Church has not yet declared it. However, from common sense and experience, we know that this issue is very confusing.
We cannot simply say, "I will donate my organs," because it depends on which organs you can donate. For example, if you can donate your kidneys but cannot donate your other life-supporting organs, you will still need them to live. So, in this case, we cannot commit any form of suicide.
We have to keep the law of God. You cannot consent to such things that entertain the possibility of killing yourself. When you take out your organs, this is against the commandment of God: "Thou shalt not kill."
There are exceptions, however, in the case of the martyrs, especially when they were taking care of the sick and contracted the disease. This is a different case because it involves an act of charity. The direct killing of a person and taking out his organs is immoral.
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