How do I make something similar to on potion effected for vanilla potions?

The title really says it all. I've tried to do this in many different ways, namely have a custom potion effect that activates whenever the player has the desired effect, and then use the 'when potion applied' prompt in the custom effect. But this didn't work for multiple reasons, so I'm just looking for a way to do this, whether in procedures or something else.