This is only a problem because people imagine a potion has to have certain traits. Afaik, none of the rules as written specify that potions have to be more than a mouthful.

It isn't like potions are medicine, where you have to have a specific quantity to be effective. They're liquid magic. A single drop could carry whatever it does, though that would be less than useful because getting that single drop out of a bottle would be just as time consuming as chugging a bottle.

If you don't think of potions as being in a half pint sized bottle, the problem takes care of itself. A vial about two inches long and an inch in diameter, made of earthenware or even glass would hold enough of whatever to fill your mouth, be just as portable, and only take three to five seconds to use.

If you ignore having to swallow, it's even faster. It's magic, it could activate and affect you as soon as it's inside your body. Which also means rectal intake would work tbh.

There's plenty of fictional reference for potions being contact based, where the first drops start whatever change occurs. And there's basis good healing positions being able to be used topically, though that won't always apply to every injury.

But think about that for a second. If the potion has to be swallowed, that's pretty badly planned magic. The healing spells that healing potions are made from are contact based depending on the system. Touch ranged healing is fairly common. So, why can the healing potions not work if poured onto a wound? Why would you have to wait while you swallow, then let the magic burst from the stomach?

And, we know potions can be used on unconscious targets. Unconscious people can't always swallow anyway. So the full draught being swallowed is obviously preconception rather than something that is inherent to potion use.

The reason potion making in our world (hey, there's recipes for them, and people think they work, don't blame me) supposedly requires drinking the entire thing is that the ingredients are part of the magic, and the use of heat to reduce the potion beyond the initial making is "magically" going to break down what would work. Mind you, that's what people have claimed when the question is posed to them.

Working with real magic, you could reduce the liquid part, or hand wave it and say that the ingredients are consumed in making the potion, and thus don't require the same end volume.

And yes, I've thought about this way too much lol

Edit: FWIW, I did some quick reading up tonight. I can't believe I've not paid attention to this in over thirty years as a DM. 5e states that a potion usually contains an ounce of liquid. A shot glass typically holds 1.25 to 1.5 ounces. There's 2 tablespoons per ounce, for another frame of reference.

So it should, RAW, only take about a second to two seconds to lift the potion vial to the lips, throw it back and swallow. That's about all it takes to do a shot.

3.X edition specifies a difference between potions and oils, so RAW potions do have to be imbibed (per the DMG) with oils being the topical version. However, it also specifies a single ounce as the quantity.

So, D&D intends potions to be slightly less than a single mouthful of liquid.

I'm not sure about TSR era as I'm not sure where to find the potion info, and PDFs of those are a bitch to look things up in. But I kinda doubt that 3.X totally threw away previous descriptions of what a potion is in terms of size