Main FAQ是有这段的
How does poisoning (or any other ability draining effect) work, exactly? Can a character get ability damage through poison several times from one monster in the same encounter? Can there be more than one secondary saving throw for poison?
First, poison causes ability damage, not ability drain. You can heal ability damage on your own (unless you lose the fight and become a monster snack), but you need magical intervention to recover ability score points lost to ability drain.
In either case, there’s no limit to the number of times a monster can beat down your ability scores with successful ability damage or ability drain attacks. Resolve each attack and apply their consequences separately. A monster could have an
ability drain or ability damage attack that could not affect the same foe multiple times, but that would be a special case noted in the monster’s description. None of the creatures in the MM have such a limitation.
In the case of poisons that deal ability damage, you must make a saving throw against the poison’s initial and secondary effects each time a poisonous attack hits you. For example, if a Huge monstrous scorpion stings you five times, you’ll have to make five initial saves and five more secondary saves, each one minute after the initial save for that attack. A character could survive a long fight with a poisonous creature only to succumb to its venom later. Smart players break out the neutralize poison spells, healer’s kits, antitoxin, or all three after encountering venomous foes.
In the case of poisons that have nondamaging effects, such as paralysis or unconsciousness, the effects don’t stack, but each one runs for its full duration.
DMG上貌似没有关于中毒效果是否可以叠加的说明
