[fellowpatriot]

Then why is it that people who undergo organ transplants need anti-rejection medication?

[gore3000]

Then why is it that people who undergo organ transplants need anti-rejection medication?

Good question. Our bodies are designed to recognize foreign intruders. The system is very specific to our own bodies, that's why to mitigate it it is often necessary to use organs from a family member with almost the same genetic structure. Otherwise it is necessary to use drugs to defeat the immune system which of course usually leads to great complications.