Wow, I didn't realize that monks in OD&D and AD&D 1E can't use potions! (And scrolls, but that didn't surprise me.) OD&D states it explicitly on page 3 of Blackmoor. AD&D 1E doesn't state it explicitly, but they are not among the allowed magic items listed (appropriate weapons, rings, and miscellaneous magic that can be used by theives) and it says all other magic items are not allowed.
I have do not know if this is how we played AD&D 1E back in the day. I have a sneaking suspicion that we missed this restriction, but I just don't know.
It was Swords & Wizardry Complete that clued me into this, as I was comparing the monk class in it with AD&D 1E, and then I confirmed it in OD&D.
There are so many differences among all the editions of pre-3E D&D! Some are quite subtle, but really change how things play: no healing potions for monks!