When you take the red pill you're not taking anything, there is no red pill, you're simply giving permission to Morpheus that you want to be taken out of virtual reality. Out of the Matrix you see that you were plugged into it with tubes feeding your nervous system with fake information, that you existed in a vat and that you were being harvested for nuclear fusion by machines. Although actually seeing this fact, the machines, the vats, the real world etc isn't enough evidence ...

When you take the red pill you're not taking anything, there is no red pill, you're simply giving permission to Morpheus that you want to be taken out of virtual reality. Out of the Matrix you see that you were plugged into it with tubes feeding your nervous system with fake information, that you existed in a vat and that you were being harvested for nuclear fusion by machines. Although actually seeing this fact, the machines, the vats, the real world etc isn't enough evidence ...