Can I cast Aid again to "heal" creatures already under the effect of the Aid spell that have been reduced to 0 HP?

Question

Suppose I have cast Aid on 3 of my allies, and those allies have all dropped to 0 hit points and fallen unconscious. I would like to get all of them back on their feet as quickly as possible. Can I cast Aid again to restore 5 hits points to each of my 3 allies who are already under the effect of another Aid spell?

I know that spells of the same name don't stack, so my 2nd casting of Aid won't increase their maximum hit points any further. However, it's not clear to me whether the hit point increase from Aid is any different from the healing provided by spells like Cure Wounds, so it's not clear to me whether there is a stacking issue that would prevent this from working.

Answer 1

At the time of casting, the second casting is the more potent effect.

The rules for combining magical effects say:

The effects of different spells add together while the durations of those spells overlap. The effects of the same spell cast multiple times don't combine, however. Instead, the most potent effect — such as the highest bonus — from those castings applies while their durations overlap, or the most recent effect applies if the castings are equally potent and their durations overlap.

Now, since the targets of the first aid are at zero hitpoints, the first aid is not currently boosting their current hitpoints by 5, so at the time of the second casting, the second casting is more potent since it would be increasing their current hitpoints when the first instance would not be.

Then after this, the “most recent effect applies” rule would apply and the second casting would effectively become the “active” effect.

Answer 2

The second aid spell won't increase its current HP more

The description of the aid spell says

Each target's hit point maximum and current hit points increase by 5 for the duration.

Therefore, while the target is under the aid effect, it has its current hit points increased by 5. When the spell is gone, current hit points will be decreased.

A second instance of aid wouldn't increase the creature's hit points twice — the most recent would take effect instead:

the most recent effect applies if the castings are equally potent and their durations overlap

Answer 3

Yes, no matter how aid is ruled

Aid says that the targets'

current hit points increase by 5 for the duration.

As written, there is a continuous effect running on the target(s) which increases their hp by 5 above what they would be without the spell. In this question, it is assumed that all three targets of the spell have their hp at zero. If the aid spell was dispelled, their hp would still be at zero. Thus, you cannot be using the spell as written if you are in this situation. If you are using the spell as written, the hp of a target can never go below 5, because if their hp would otherwise be at 0 without the spell, the spell should be providing a continuous effect that raises their current hp for the duration. (This is in the same way that the continuous effect of gauntlets of ogre power keep your strength at 19 even as you are being temporarily drained of strength by a shadow)

A popular and accepted work-around to this problem posits that the continuous effect on current hp of the aid spell is not the increase of five for the duration, as written, but rather is a more complicated effect that increases the hp by 5 when it takes effect, does nothing for the bulk of the duration, and then at the very end of the duration actively reduces the hp by 5. If this is how aid works for the three targets at 0hp, then a second casting of aid would introduce a second and overlapping identical continuous effect. Because both effects are equally potent, the more recent one - the second casting - would be in effect while the first casting would be suppressed. In this case, as a 'start of duration' effect, all three targets would have their current hp increased by 5, in effect 'healing' them.

Another way to run the spell not as written acknowledges that you cannot sensibly have a continuous effect affecting current hp, because current hp is not a base value to which ongoing continuous affects are applied. In this case, the hp gain from aid is treated as a one-time instantaneous effect, such as in heroes' feast, rather than as a continuous effect. If this is how aid works for the three targets at 0hp, then a second casting of aid would introduce a second one-time increase, which would not involve the simultaneous effects rules, and all three targets would have their current hp increased by 5, in effect 'healing' them.

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No matter how you run aid, this should work. If you run aid as written, you will not be in the situation of three targets at 0hp to begin with. If you run it as a continuous effect hp 'loan', the second casting will increase the target hp, as will a second casting run with the current hp increase as an instantaneous effect.

Answer 4

Yes, but be careful.

When you cast the second Aid spell on them, the first one is suppressed, and they lose the 5 HP it granted them. Because they are already at 0 HP, this damage causes them to automatically fail a death saving throw. They are then healed 5 HP by the new Aid spell.

As a result, if they have already failed 2 death saving throws, casting a second Aid spell will cause them to fail 3 death saving throws and kill them. If they haven't, then the healing will kick in and they'll be revived at 5 HP.