Can the Midnight Tears poison be split into a handful of drinks to affect many targets?

Question

I have an evil PC in my game that, as the DM, I want to assist in making a surprise against the other players. The idea is that they go to the tavern and have a few drinks before the big final battle we have planned. During this time, the rogue in their party is going to slip Midnight Tears poison into their drinks, using a sleight of hand check to successfully do it.

My question is, he has only 1 vial of this poison. Can one vial be divided into 4–5 drinks and still inflict damage on all of them equally?

Midnight Tears (Ingested). A creature that ingests this poison suffers no effect until the stroke of midnight. If the poison has not been neutralized before then, the creature must succeed on a DC 17 Constitution saving throw, taking 31 (9d6) poison damage on a failed save, or half as much damage on a successful one.

Answer 1

A dose cannot be split unless the DM states otherwise.

Consider p258 of the DMG (emphasis mine) in purchasing poisons. The pricing on that table is per dose. It also states that in order for the poison to have an effect the victim must consume the entire dose. So unless the rogue in question purchased a dose for each of the other PCs he would not be able to poison all of them, again unless the DM indicates partial effects are plausible. Since Midnight Tears seem to have a pseudo magical component to its efficacy it would seem implausible that this would have a partial effect, but table mileage will vary.

Ingested. A creature must swallow an entire dose of ingested poison to suffer its effects. You might decide that a partial dose has a reduced effect, such as allowing advantage on the saving throw or dealing only half damage on a failed save.

On the following page.

The Poisons table gives suggested prices for single doses of various poisons.

Answer 2

The DMG says no, with caveats.

DMG 257:

A creature must swallow an entire dose of ingested poison to suffer its effects. You might decide that a partial dose has a reduced effect, such as allowing advantage on the saving throw or dealing only half damage on a failed save.

Answer 3

The 5E Dungeon Master's Guide states:

A creature must swallow an entire dose of ingested poison to suffer its effects. You might decide that a partial dose has a reduced effect, such as allowing advantage on the saving throw or dealing only half damage on a failed save.

So, as DM, you are allowed to rule that the potion can be divided - but if you do, it shouldn't be as potent as the full dosage.

I'd recommend that you divide the total 9d6 damage by the number of drinks the vial was split between. Then have each infected PC roll the CON save, perhaps at advantage (since the poison's potency was reduced).