In Chapter 9 of the game - The Town That Never Sleeps, you will reach the Corneo Colosseum at some point. Before the battles you will be offered a mystery drink - you can choose whether you want to drink it or not. So, is it worth drinking it? This page of our guide to FF7 Remake answers this question.
As it turns out, drinking the potion has absolutely no meaning at all. If you drink the potion, you don't get any buff/debuff, your stats don't change and it won't affect the course of the battle. Cloud will just make a comment about the taste of the drink in front of Aerith.
Therefore, you can choose any option without fear - it will not change the course of the plot in any way. You will just have a brief conversation with Aerith and Johnny. After that, you can prepare yourself for the upcoming battle at the Corneo Colosseum.