"I Wouldn't Drink That If I Were You"
Way back in 1st edition Dungeons & Dragons, there was a concept called Potion Miscibility, which addressed what happened when you drank a second (or more) magic potion while the effect of a first was still active. This concept made its way into 2nd edition, but disappeared from the 3rd edition of the game. Why? Well, potions are now very specifically defined as liquids carrying spell effects, and since a person can have more than one spell affecting her at once, she can have more than one potion effect affecting her at the same time. Logical, no? This makes the game simpler too, since you can just buy liquid spells and buff up when you need to... without worrying about exploding.
However, the Potion Miscibility rules from the older editions were still great fun, and no doubt contributed to some memorable events in characters' lives (or the end thereof). So for those of you that like a little risk in your magic use, break out your figurative Russian Roulette pistols. We cast raise dead on those dearly departed Potion Miscibility rules, updated them, and present them as an option for use in your campaigns.
Mixology of Magical Liquids
The first issue is, of course, "can you mix potions at all?" If you cannot mix them, then you don't need to worry about strange effects if they mix. Sages have discovered that this is more complicated than simply "yes" or "no." You cannot mix potions... but under certain circumstances you can. What can we say? Magic is confusing like that.
Potions are liquids that carry magic, and as such they resist mixing with other potions or with mundane liquids. So on the passive level, they don't mix. Each potion has a potential energy threshold against mixing, if you like to think in those terms (that's the easiest explanation, anyway). If you pour two or more potions into the same bowl, for example, you get a number of separate liquid blobs that sit next to each other and don't mix. If you pour two or more into a large vial, you get layers of different potions that remain distinct.
However, that's on the passive level, and the purpose of today's article is to look at what happens when you do mix potions.
If you can overcome their potential energy, you can mix potions. This happens in two known circumstances. The first is when you vigorously shake or stir a container holding two or more potions; you have to do this for two minutes, but eventually you get the liquids to mix. The second is, of course, when you drink multiple potions (remember, these are optional rules; normally, you may drink as many potions as you like without consequence). Your body starts breaking down the easily digestible magical liquids immediately, and as they break down, their energy bar against mixing lowers. This is why people sometimes worry about having the magic of more than one potion affecting them at the same time. Strange things could happen.
What Can I Do With Mixed Potions?
Problems of Combination
There are three things you might reasonably do that would involve combining potions. The first is to carry two or more potions in the same vial. Adventurers long ago thought that this would be a good way to drink several potions at once, assuming nothing bad happened when they were put into the container in the first place. And they tried, many times, with mixed results (no pun intended). Because they don't mix in a passive state, you can carry more than one potion in the same vial, provided you have a big enough vial. Each potion is one ounce, and potion vials are made to carry one ounce. If you want to carry more, you have to have bigger bottles made.
When several potions are added to the same vial, they layer in the reverse order that they were added, so the most recent is on top. For example, if you have a big vial to which you add a potion of fly, a potion of shield of faith +4, and a potion of cure light wounds, then they layer in the vial in that order. The consequence of this is that you must drink them in the order they are layered top to bottom, since they don't move around in the bottle for you.
You could use this layering property to create a big vial and drink a lot of potions at one time. And if you can do that, you might as well layer in six potions of cure light wounds into one vial rather than have a single potion of cure moderate wounds. But, it doesn't work quite that way. Adventurers have found that no matter how many potions they have in a vial, drinking one potion is a standard action and each layer counts as a separate potion. Thus, if you have a vial with the above three potions, it takes three standard actions to drink them. Magic liquid is like liqueur, not beer; you cannot chug it. So, if you want to carry your potions in one vial, you have to decide whether the advantage of having only one vial to grab outweighs the disadvantage of having to drink them in a certain order that may not meet your needs.
One important thing to remember is that vigorous motion could mix the potions while you are carrying the vial. If you ride horse at a bumpy gallop, for example, you could end up with a mixed potion. If so, see "What Happens When They Mix?" below.
Problems of Division
Another thing you might want to do is divide up your potion, and make several doses of a weaker potion from a single dose of a stronger one. For example, you might want to make your potion of cure serious wounds into three potions of cure light wounds to better spread its healing capability. Yes, you can dilute a potion, but this is not as easy as you might think.
First of all, you have to figure out what the solvent is. Not all potions are made with a water base, you know. The base might be oil, alcohol, vinegar, or insect stomach acid, hill giant eye fluid, or something even more vile. You can only dilute a potion in the same solvent that forms its base, so if you want to dilute on the fly you should carry around the more common potion solvents. To figure out the solvent, break out your alchemical gear and spend an hour analyzing. Then make a Craft (Alchemy) check (DC 25) to realize what you need. Adding a different solvent destroys the potion.
Second, you have to dilute by exact concentrations, so you have to add units of exactly one ounce. This requires a measuring container such as would be found in an alchemical lab. Adding any different amount (say, an ounce and a half) destroys the potion.
Third, you can only dilute potions so that they retain whole die numbers of effect (when the potion has an XdY effect, such as a potion of cure serious wounds) or the minimum duration as if a 1st level caster created it. And the effects of the potion are divided evenly among all the dilutions (round down). For example, you could dilute a potion of cure serious wounds into thirds but not halves, because you cannot dilute it to 1.5d8 per dose. You could dilute a standard potion of fly into fifths, each part lasting 1 minute. In this case, each dose would give a speed of 12 ft, which rounds down to 10 ft. because all movement has to be in units of 5 ft. You could dilute a standard potion of bull's strength into thirds, each lasting 1 minute and granting a +1 enhancement bonus to Strength (rounded down from 1.33).
That's pretty complicated, and probably not worth it most of the time. But it could get you quite a laugh or two when you sell a diluted potion of fly as a full-strength one and watch the poor buyer fly off at slow speed.
Problems of Addition
The last thing you might want to do is to drink several potions and enjoy all their effects at the same time. This is very helpful when your party lacks the spellcasters to properly buff you for a combat. This is where you are most likely to run into problems with mixing, so knowing when to check for compatibility problems is important.
When Do I Check for Compatibility?
The first thing to consider in checking for potion incompatibility is when to check. Do all potions require checks? Let's look at some cases.
Case 1: You drink a potion with a duration of instantaneous, such as a potion of remove curse, and no other potion's magic is affecting you. You can drink another potion in the next round because the magic of the first is not affecting you by the time you drink the second.
Case 2: You drink a potion with a duration that is not instantaneous. Then you drink a second (different) potion. You need to check for compatibility unless the second is a curing potion (e.g., a potion of cure light wounds, etc.). Curing potions always work and never interfere with other potions; we don't need to complicate the process of healing during a battle.
Case 3: You drink a potion, and then when its duration is almost over you drink a second of the same kind, to keep the effect going. This would occur when flying and needing to recharge your flying capability, or when a rogue is hiding in a mark's house and drinks successive potions of invisibility to remain unseen. In this case, you need to decide which approach you are going to take to potion making.
The basic rule is this: If the potions are either made the same way, or they are curative, then you don't have to check for compatibility. If the potions are not made the same way and none of them are curative, then you have to check. How do you determine whether your batch of three potions of fly were made by the same maker? Take a drop of each and use your Craft (Alchemy) skill and your alchemical apparatus. A successful DC 25 check (representing one hour of analysis) tells you exactly what is in each, and if they have the same ingredients in the same concentrations they were made in the same way.
What Happens When They Mix?
Now that you've drunk two potions that require a check to see if they are compatible, or have accidentally (or purposefully) mixed potions in a vial, let's discuss exactly what happens to you.
When you drink potions that require compatibility checks, the DM secretly rolls on the table below, and afflicts you with the resultant entry from Table 1-1 below. Some are good, some are horrible. Mixing potions is kind of like a rod of wonder in that way.
Three useful numbers for the result table are the following:
Table 1-1: Potion Compatibility Results
There you have it--all about mixing magical potions in Dungeons & Dragons. It's a bit more complex than mixing drinks in a bar, that's for sure. It's difficult to "slip someone a mickey" using a potion, but I should point out in closing that whoever designed the philter of love knew how it would be used, and created it with a water base. Thus, it can safely be added into any other mundane beverage (all of which have water as a base) and slipped to someone. Sure, the philter is diluted, but if the victim drinks the whole beverage then he drinks the whole potion. If the beverage is shared, well... that could be fun too.
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