Antimetabolites are like pretend friends that look almost like your real friends, but they don't play nicely together. Our body requires certain substances to grow and reproduce, like building blocks in legos. Antimetabolites are chemicals that pretend to be some of these building blocks, but once they are inside the body, they don't fit quite right. It's kind of like trying to put a square block into a round hole. When cells try to use the antimetabolites instead of the real building blocks, it causes them to dysfunction, stop growing or die. So, doctors may use them as a treatment for diseases like cancer. It helps slow or stop the growth of the tumors, which can lead to treating cancer.