When you drink this potion, you gain the “reduce” effect of the Enlarge/Reduce spell for 1d4 hours (no Concentration required).
The red in the potion’s liquid continuously contracts to a tiny bead and then expands to color the clear liquid around it. Shaking the bottle fails to interrupt this process.
RollQuest summary "Reduce" effect of Enlarge/Reduce for 1d4 hours (no Concentration): size decreases one category, Disadvantage on Strength checks and Strength saving throws, and attacks with your reduced weapons or Unarmed Strikes deal 1d4 less damage (minimum 1).
RollQuest ships the D&D 2024 SRD as a content pack, on a 5e character sheet that does the maths - roll from the sheet and let the numbers work themselves out. Free to start.