It's well documented that in 5e, you can deal 0 (but not negative) damage on an attack roll, usually if you have a negative ability modifier. The same, presumably, would apply to spell damage.
A 1st-level Cure Wounds restores 1d8+spell mod in hit points. What happens if I have a -2 modifier, and roll a 1? Would it heal 0 hit points? Would it stabilize a dying character?
Official sources (or tweets from Crawford) preferred.
Best Answer
Designer's Intent
Mike Mearls tweeted that it should be a minimum of 1 point, but I can't find the same from Jermey Crawford. Mike Mearls talked about what was intended, but it isn't an official ruling:
Jeremy did weigh in about hit dice though:
If Mike is right about this spell, then the player becomes stable. If Jeremy's tweet about Hit Dice also apply to spells like cure wounds there would be no reason to assume that healing for 0 would stabilize someone, as the spell text doesn't say anything of the sort; but I think as a DM I'd let it.
Updated Text of Hit Dice and RAW
When the question was asked Jeremy's tweets were considered official rulings. Since then the text of regaining health from hit dice was edited in later editions since the question was asked to include:
The text of the spell was not updated. So the only clues we have about cure wounds is the word "regain" in the spell, which implies it cant' be negative, and the intent text above. Unless a word has a special game meaning, the common definition applied. Oxford Languages Dictionary offers the following definition:
You can't obtain possession or use of negative hit points. Any argument must also use that common meaning standard. So when the rules say things like:
It is telling you what to do, add them to your total, after you regain them. This doesn't change the meaning, define or redefine the word regain.