[RPG] How does the Life Drain ability of the Wraith and Specter interact with temporary hit points

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Wraiths have the Life Drain action; on a hit, it forces the target to make a Con save to avoid having their max HP reduced:

The target must succeed on a DC 14 Constitution saving throw or its hit point maximum is reduced by an amount equal to the damage taken.

Specters also have a similar ability.

Temporary hit points are said to protect you from injury.

Temporary hit points aren't actual hit points; they are a buffer against damage, a pool of hit points that protect you from injury.

Will Life Drain's max HP reduction work if the damage you take is less than the temporary hit points you have?

Best Answer

Life drain's effect is the same with or without temporary HP

Rules as Intended: Damage to temporary HP still counts as damage

Per this Jeremy Crawford Tweet:

When temporary hit points absorb damage for you, you're still taking damage, just not to your real hit points.

So, when the Life Drain ability says "hit point maximum is reduced by an amount equal to the damage taken" that means that max HP will be reduced by the amount of damage done regardless of temp HP.

So, the temp HP absorbs as much damage as it is able to absorb, but that damage is still considered taken (no matter how much or little temp HP you have). Then, that damage number (which again is unaffected by how much temp HP you had), is subtracted from your HP maximum. Your current HP will also be reduced if the HP maximum is reduced to below your current HP.

Jeremy Crawford has agreed with this interpretation in this tweet:

Q: You are hit by a Specter's Life Drain for 10 damage. You have 8 temporary hit points. Is your Max HP lowered by 2 or by 10?

A: By 10

So, to answer you question directly:

Yes, Life Drain's max hp reduction will work if the damage is less than available temporary hit points.