One of my players just got the Shield spell, which has a cast time of 1 reaction. I realized that I always thought, reactions were automatic. But since Shield is a level 1 spell, this would be quite unfair, as it could drain your spell slots pretty fast.

Is there any ruling on whether you have to take a reaction when you have the chance to? I couldn't find anything in the rules and a quick Google search also didn't reveal any existing questions on the matter.


3 Answers 3


You generally choose whether to take a reaction

In general, each opportunity to use your reaction is a choice. The rules don't spend a lot of words on this, but the wording consistently uses the word "can", which gives a clear implication that you can choose to not. For example, the rules on opportunity attacks state (PHB/BR Chapter 9 > Actions in Combat > Melee Attacks; emphasis added)

You can make an opportunity attack when a hostile creature that you can see moves out of your reach.

So, while the trigger description for shield doesn't include that, the choice is established by the general rule on casting times for spells (PHB/BR Chapter 10 > Casting a Spell > Casting Time):

If a spell can be cast as a reaction, the spell description tells you exactly when you can do so.

This probably doesn't come up that often outside of spells or Readied actions, as you'd normally just want to take opportunity attacks at the first opportunity.

There's an obvious set of exceptions to the above, which are features and spells which force the use of reactions. For example, the description of the dissonant whispers spell includes the effect:

[...] and must immediately use its reaction, if available, to move as far as its speed allows away from you.

which clearly leaves no room for the creature to choose, but it'd be really weird for your own spell to similarly force you to use your reaction. Not to mention what kind of liability counterspell would turn into.

  • 1
    \$\begingroup\$ Some good examples might be not taking a melee OA to keep their reaction open for Counterspell, or a grave cleric keeping open the option to cancel a crit. (Harder tradeoff if they have a good melee attack, like a hexblade.) Or not using your Sentinel reaction when an enemy attacks someone else, so you can try to stop it from leaving with an actual OA triggered by movement. (Which would set its speed to 0 for the rest of the turn.) \$\endgroup\$ Mar 6, 2022 at 7:35

Reactions are not automatic

The rules on reactions state (emphasis mine):

Certain special abilities, spells, and situations allow you to take a special action called a reaction. A reaction is an instant response to a trigger of some kind, which can occur on your turn or on someone else's. The opportunity attack, described later in this section, is the most common type of reaction.

When you take a reaction, you can't take another one until the start of your next turn. If the reaction interrupts another creature's turn, that creature can continue its turn right after the reaction.

The wording "allow you" indicates it is a choice, and that is backed up by the restriction of one reaction per turn.

It is a resource for you to manage, not something that is free or automatic.


You can ignore triggers

Both Someone_Evil and Willem Renzema quote relevant rules texts in their answers and are correct in their interpretations.

For me, the clearest statement that reactions are optional comes from the rules on readied actions (emphasis mine):

When the trigger occurs, you can either take your reaction right after the trigger finishes or ignore the trigger. Remember that you can take only one reaction per round.

I like this passage because it explicitly establishes that one can refuse to take a reaction, rather than having that be implicit through the use of 'can' and 'allow' when describing the positive choice to take a reaction as the rules cited in the other answers do. By preferring it, though, I am assuming that the rules for taking reactions permitted by readied actions are no different from those of any other reaction. I don't know why they wouldn't be, but it is a fair objection if one doesn't want to assume that.

The passage establishes that each time you have the ability to take a reaction due to a trigger, you can decide to do so, or not. This is a strategic decision since using your reaction for that particular trigger then removes the possibility of reacting until your next turn, while not using it preserves your ability to respond with a reaction to any other trigger that occurs until then.

Your intuition that forced reactions would drain spell slots is correct. Consider also any melee character that closed the distance to an arcane caster - if one were required to take any available reaction, it would be trivial for you to move into the caster's reach, then move out again to force them to make an opportunity attack (with what? a dagger?) and then move back in again, confident that they could no longer use their shield spell to protect against your attack. This would considerably reduce the power of the shield spell, as well as many other abilities that either force your opponents to take reactions or remove their ability to do so.


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