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