An IPotionEffect is an IPotion that also has a duration and an amplifier (strength) parameter.
You can get them from an IPotion object.

It might be required for you to import the package if you encounter any issues (like casting an Array), so better be safe than sorry and add the import.
import crafttweaker.potions.IPotionEffect;

ZenGetter	Tipo
ZenGetter duration	Tipo int
ZenGetter potion	Tipo IPotion
ZenGetter doesShowParticles	Tipo bool
ZenGetter amplifier	Tipo int
ZenGetter curativeItems	Tipo List<IItemStack>
ZenGetter effectName	Tipo string
ZenGetter isAmbient	Tipo bool
ZenGetter isPotionDurationMax (also a ZenSetter)	Tipo bool

Uses an IItemStack.
Returns a bool

ZenScript
 Copy
isCurativeItem(IItemStack item);

Uses an IEntity or any of its subclasses (e.g. IPlayer).
Returns void (nothing).

ZenScript
 Copy
performEffect(IEntity Entity);