DMG Reflections: Potion Miscibility

Mage Hand is a handy spell after all!

I've said this before, the 1st edition Dungeon Master's Guide is my favorite D&D book of all time. I know I'm not alone in this sentiment. There's not a dull day that goes by that I can't pick up this book, flip to a random page and find something in it that I don't ever remember reading. The DMG is mostly packed with information useful to gaming yet often there are entries that are so esoterical that they border on useless. But that's the beauty of the DMG, because once in a blue moon a situation might arise in a DM's game and lo and behold Gygax has it covered. One of these oddly improbable situations is the Potion Miscibility Table (Pg 119).


"The magical mixtures and compounds which comprise potions are not always compatible. You must test the miscibility of potions whenever:

1) two potions are actually mingled, or
2) a potion is consumed by a creature while another such liquid already consumed is still in effect.

...it is suggested that the following table be used - with, perhaps, the decision that a 'delusion' potion will mix with anything, that 'oil of slipperiness' taken with 'oil of etherealness' will always increase the chance for the imbiber to be lost in the Ethereal Plane for 5-30 days to 50%, and 'treasure finding' mixed mixed with any other type of potion will always yield a lethal poison. Whatever certain results you settle upon for your campaign, the random results from the table apply to all other cases."

This level of detail can only be found in old school D&D. As the editions rolled on by, drinking multiple potions became as superfluous as drinking different colors of kool-aid, while mixing two potions together in the same container is an unthinkable action to today's gamer. But with the Potion Miscibility Table there is some interesting side effects that a gambling player could exploit:

• (01) EXPLOSION! Internal damage is 6-60 h.p., those within a 5" radius take 1-10 h.p. If mixed extenally, all in a 10' radius take 4-24 hit points, no save.
• (02-03) Lethal poison results, and imbiber is dead; if externally mixed, a poison gas cloud of 10' diameter results, and all within it must save versus poison or die.
• (04-08) Mild poison which causes nausea and loss of 1 point each of strength and dexterity for 5-20 rounds, no saving throw possible.; one potion is cancelled, the other is at half-strength and duration.
• (09-15) Immiscible. Both potions totally destroyed, as one cancelled the other.
• (16-25) Immiscible. One potion cancelled, but the other remains normal (random selection).
• (26-35) Immiscible result which causes both potions to be at half normal efficacy when consumed.
• (36-90) Miscible. Potions work normally unless their effects are contradictory, e.g. diminution and growth, which will simply cancel each other.
• (91-99) Compatible result which causes one potion (randomly determined) to have 150% normal efficacy. (You must determine if both effect and duration are permissible, or if only the dureation should be extended.)
• (00) DISCOVERY! The admixture of the two potions has caused a special formula which will cause one of the two potions only to function, but its effects will be permanent upon the imbiber. (Note that some harmful side effects could well result from this...)        

There you have it. The drawbacks seem to outweigh the advantages, but if you think about that one in a hundred chance of a permanent effect from mixing two potions, it goes a long way to explaining things in canon like the extraordinary abilities and lifespans of quasi-deities like Heward, Murlynd and Keoghtom, or the abundance of transformed monstrosities like liches, animus, mongrel-men and some yuan-ti. The Potion Miscibility Table is not hard to implement in any edition and I guarantee it'll add an air of suspense to these items that players take for granted.