The Potion of Poison has the following description:
This concoction looks, smells, and tastes like a potion of healing or
other beneficial potion. However, it is actually poison masked by
illusion magic. An identify spell reveals its true nature.
Now, does this mean that an Identify spell is the only way of finding out that the potion is actually a poison, or would a spell such as Detect Poison and Disease also work?
you can sense the presence and location of poisons, poisonous
creatures, and diseases within 30 feet of you. You also identify the
kind of poison, poisonous creature, or disease in each case.
To me, the following two interpretations seem just as likely:
- The "illusion magic" can trick spells such as Detect Poison and Disease, but not Identify.
- It was obvious that Detect Poison and Disease would work and only the interaction with Identify needed to be mentioned, since Identify usually doesn’t work on poisons.
Best Answer
Detect Poison or Disease works, but ask your DM
The item description only states that the potion looks, smells, and tastes like a potion of healing or other beneficial potion, it does not say that it is immune from magical detection effects. Therefore, by default divination magic will work on it.
The item description tells you that An identify spell reveals its true nature, it does not say "Only an identify spell...". The way it is worded, other ways of finding out about its true nature are not excluded by mentioning Identify.
So why mention identify? The potion is not a cursed item like other "gotcha" items. Being cursed would make it immune from most methods revealing its true nature, including Identify. It is possible that Identify has been called out to work, just to avoid ambiguities in this regard. (Or, as Kirt's answer points out, it could be because normally there is a faster way to find out by taste, that does not work here).
From a balance perspective, both Identify and Detect Poison and Disease are first level spells, so it is not as if you were using a much cheaper effect. To the contrary, Identify can be cast as a ritual, which would not even consume a spell slot (although it has a moderately costly, reusable component).
Your DM might decide otherwise, as in earlier editions of the game such potions used to be treated like cursed items, and they may want to uphold the "gotcha" effect such items have. On the other hand, if you are careful enough to use a spell, it would seem fair that you get the benefit of not falling for the trap. Check with your DM.