Can a creature be brought to consciousness while they have a max HP of 0?

Question

As explored in this question there is at least one situation where a character’s Max HP could be reduced to 0 without explicitly or immediately killing them. We've recently been looking into what does happen when the cause of such a situation is rolling poorly when leveling up or simply having an incredibly low Constitution score, and it seems pretty clear they fall unconscious (and potentially begin rolling death saves). We've also established elsewhere that temporary hit points don't bring you to consciousness if you're at 0 HP.

Let's assume that a character has taken a hit to their max HP for whatever reason and therefore is now a mid-level character with 0 max HP. Could an especially dedicated party keep them around and conscious in any way while searching for a cure?

I had a think and came up with a potential 3 part process to achieve this:

1. Cast false life on the character, giving them 1d4+4 hit points for one hour. At this point she is still unconscious.
2. Cast cure wounds on her, which won't give her actual hit points, but may still bring her to consciousness as she has temporary hit points from false life (though these comments suggest that might not work.)
3. In order to keep her conscious, cast heroes' feast to give temporary hit points that will last 24 more hours. (We cast false life just to give enough time to benefit from heroes' feast as common sense suggests someone who is unconscious cannot meaningfully partake in a feast of any sort.)

My only concern here is that I'm not sure if coming back to consciousness as a result of a healing spell like cure wounds is dependent on acquiring actual hit points.

Could a party member be kept functional indefinitely (regardless of the cost) until a permanent way of recovering from the Constitution score hit could be found?

Answer 1

If their maximum hit points is zero then healing magic won't do anything. Healing magic allows a character to "regain" or "restore" hit points, which is always up to your maximum.

When a creature receives healing of any kind, hit points regained are added to its current hit points. A creature's hit points can't exceed its hit point maximum, so any hit points regained in excess of this number are lost.

Basic Rules, Combat chapter.

This disallows cure wounds and healing word and their mass versions, prayer of healing, goodberry (assuming you can feed a berry to an unconscious person) and pretty much all healing potions.

One spell that will help is aid - as long as you keep casting it over and over again.

Your spell bolsters your allies with toughness and resolve. Choose up to three creatures within range. Each target's hit point maximum and current hit points increase by 5 for the duration.

Please note that many effects that reduce maximum hit points also specify really bad things for when the character reaches 0 (for example, the strength drain attack of a shadow). Keeping someone conscious isn't much of an issue when they've turned into an undead monster and are trying to eat your face.

Answer 2

The only way to bring an unconscious creature to consciousness is by causing it to regain hit points

If damage reduces you to 0 hit points and fails to kill you, you fall unconscious. This unconsciousness ends if you regain any hitpoints. - PHB 197

If we're taking that to be an apt description of what happens when max HP drops to 0 as well, regardless of whether it's caused by damage (a semantic question explored somewhat here) then the only way to end this condition is by regaining hit points. The only references to unconsciousness in the PHB to that do not relate to taking damage that reduces your hit points to 0 come from spells and effects that essentially put you to sleep, with specific wording around how their effects work and can be ended:

• Astral Projection (PHB 215)
• Eyebite (PHB 239)
• Sleep (PHB 276)
• Symbol (PHB 280)
• pseudodragon's Sting attack (PHB 308)

The suggested method cannot do this

Temporary hit points aren't actual hit points

Temporary hit points aren't actual hit points; they are a buffer against damage, a pool of hit points that protect you from injury. [...] If you have 0 hit points, receiving temporary hit points doesn't restore you to consciousness or stabilize you. - PHB 198

This aligns with what was discussed in this answer linked in the question.

You can only regain hit points up to your hit point maximum

When a creature receives healing of any kind, hit points regained are added to its current hit points. A creature's hit points can't exceed its hit point maximum, so any hit points regained in excess of this number are lost.

Healing spells only bring creatures to consciousness by virtue of causing them to regain hit points. I searched for the word "unconscious" in the PHB, and aside from the examples listed above, and references to creatures that are already unconscious being excluded from certain effects, it's never mentioned. No method of regaining consciousness besides regaining hit points is ever given.

A creature with 0 max hit points can only be brought to consciousness by increasing their max hit points

Because the only way to regain hit points is to have hit points to regain in the first place, there is no way to bring a creature to consciousness while they have a 0 hit point maximum. There are likely to be many potential ways to raise their max HP, but the PHB only provides a few. For clarity, these solutions will not bring a character to consciousness while they have a max HP of 0, but will rather raise their max HP either temporarily or permanently. In decreasing order of likely suitability:

• As mentioned in other comments, the spell Aid will do this for 8 hours at a time.
  • This seems to fit with the intent of band-aiding the problem until an actual solution can be found.
• If some effect caused you to somehow take a hit to your Constitution score, and that's why your max HP has dropped to 0, Greater Restoration may be able to end this effect.
  • This seems more like what you'd be aiming for ultimately, rather than a stop-gap measure to allow the afflicted character to have agency in their own restoration.
• Wish is a potentially more lasting option as it can increase your Constitution score permanently.
  • As a more final solution, this might also be what you end up with after getting by on Aid for a while. It's a higher level spell, though.
• If you're lucky, Reincarnate could change you into a Dwarf, or some other race that gives your constitution score a bump, giving you the same max HP benefit as Wish would.
  • This one only really works if you're happy to roll the dice (heh) on this issue. And if you weren't already a dwarf to start with.

Answer 3

No, you cannot bring a creature to consciousness while their max HP is 0

Dropping to 0 Hit Points

When you drop to 0 hit points, you either die outright or fall unconscious, as explained in the following sections. (Basic Rules)

Your process above will not work as none of those steps change the creatures Hit Points (not temporary hit points which are completely different) from 0HP. Here's what will happen.

1. Still unconscious. 0HP/0HP + (1d4 + 4) Temporary HP

False Life is temporary hit points, which you've already confirmed do not return a creature to consciousness.

2. Still unconscious. 0HP/0HP + (1d4 + 4) Temporary HP

Healing cannot raise your HP above your max HP. If your max HP is zero, then healing can stabilize the creature, but not return them to consciousness.

The best way to save a creature with 0 hit points is to heal it. If healing is unavailable, the creature can at least be stabilized so that it isn't killed by a failed death saving throw.

[...]

A stable creature doesn't make death saving throws, even though it has 0 hit points, but it does remain unconscious. (Basic Rules)

3. Still Unconscious. 0HP/0HP + (1d4 + 4) Temporary HP

The feast takes 1 hour to consume [...] A creature that partakes of the feast gains several benefits. (Basic Rules, pg. 250)

A creature must 'partake' in the feast for an hour. Since partake is not a game term we use the normal definition of partake, which is to eat or drink (both active) or to join in an activity. An unconscious creature cannot actively partake in anything, let alone for an hour.

The only way to return consciousness to an unconscious creature is to let it gain 1 or more HP or to kill it and use some sort of resurrection or revivify spell. Note that all of the resurrection spells I could find in the PHB do NOT increase your maximum HP, so they would not actually revive a creature that is not conscious due to having a maximum of 0HP.

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Aid is the only option I could find that would actually help get a 0HP max creature up without directly addressing the issue that caused their HP max to drop to 0. A second level spell that increases max HP by 5 for 8 hours.