Does water reduce the effects of medicine?

People usually take a sip of water after drinking medicine cus it's to clear the sweetness of the teeth to avoid toothache rite? I'm just concerned about the part when the medicine is travelling down the throat, the solution is thicker and travels slower, water travels faster down and would easily catch up with the medicine and dilute it, but then medicine is alkaline, and water is neutral, you would need acid to decreace the ph level of alkaline, so how would *nuetral* water affect it?