Does damage from an ally break Dominate Person?

Question

Dominate Person states the following:

Each time the target takes damage, it makes a new Wisdom saving throw against the spell. If the saving throw succeeds, the spell ends.

As written, this would presumably include damage from an ally - am I right?

From a gameplay perspective, this is a great boon to players who lose a team member to a vampire (or whatever) since it is a lot easier to damage the ensorcelled player with ranged or AoE attacks than with a greater restoration which is a touch spell. Nothing in the Vampire's Charm description indicates that it is different from the Charm spell; it does specifically refer to it as magic, rather than innate.

Is there something that I am missing?

Answer 1

If it takes damage, it gets a saving throw

Damage from allies is not automatically distinguished in D&D 5e, so yes you could damage your own allies to break a spell. Unless the spell specifically states that the damage must come from a specific source, it means all sources. This is a valid strategy and part of the balance of the spell.

As you've rightly pointed out, the description of the Vampire specifically outlines the difference between who is damaging the charmed target.

Each time the vampire or the vampire's companions do anything harmful to the target, it can repeat the saving throw

While "harmful" is less specific than "takes damage", you can see that a distinction has been made between any attacker and the Vampire's companions, and thus the absence of such a clause in Dominate Person indicates that any damage will trigger a saving throw.

Keep in mind that you can't predetermine how much damage you're doing to a friendly creature. If you crit, you crit. If you deal max damage, you deal max damage. You could, of course, make an unarmed attack and deal 1+STR_mod damage, since there are no dice to be affected by a critical hit, or use an improvised weapon which deals 1d4 + proficiency bonus damage.

Answer 2

Dominate spells, yes. A Vampire's Charm, no.

A Vampire's Charm isn't a spell, or stated to be equivalent to a spell. Other monster abilities say "affected as if by a [insert spell here] spell", those abilities do work the same as the stated spell, unless stated otherwise. The Vampire's Charm has no such wording.

The description of it as magical also doesn't mean it's equivalent to any spell - it just means that it's a magical effect, and therefore affected by spells such as antimagic field. Spells are magical effects, but not all magical effects are spells.

Dominate Person/Monster includes wording stating that the target gets additional saves if they take damage, without any stipulation about who deals that damage or what kind of damage it is. So any source of damage, including from allies, can break the effect.

In contrast, a Vampire's Charm action says that they get additional saves if damaged by the vampire or the vampire's companions. Therefore the other player characters can only break a vampire's charm by damaging the person if they are (perceived by the target to be) companions of the vampire.