I'm back so how about this
Hard cap the number of potions to three to four and they must be ST-Approved and in the users inventory.
No lore targetting/limiting a group, no lore stating a group will face backlash, just a hard bloody cap. Not everything and its mother needs a lore amendant to say who can do what and not, just state oocly there's a hard cap on how many potions you can carry because people are carrying inventories full of potionsd leave it at that. That way, it ensures everyone is limited to having specific potions, having to think what potions they're carrying on them, and affectes EVERYONE.
[Edit] Here's another idea - Allow Alchemists a chance to stablize their potions! If their potion starts acting up while in the presence of a connected voidal mage - let the alchemist have a chance in making sure that vial doesn't explode on them and a chance to still use it. Make it a roll requirement of above a 10 or 15 depending on if its a beginner potion or a master potion. Just give the Alchemists a chance to be able to prevent a disaster, as they should have the skill to prevent it!
This lore is targetting one group - not everyone, not addressing or fixing the issue, it is targetting one group. It's like slapping a bandaid on a life-threatening wound - it looks like it's helping, but it isn't. Can we just please stop with lore that outright restricts a group for a problem that is happening with every single bloody group!
This is why I love you, Delmo. THIS ^
If this lore amendant doesn't look like specific targetting, I'm not sure what will. Holy magic and dark magic should also affect a potion, if we're going down this route. Deity magic isn't natural and is bound to conflict with the potions the same way Voidal conflicts, as with some dark magics.
So, for the love of this old alchemist player who would rather see Alchemy made avaliable for everyone to enjoy - as I am sure Jistuma himself would too - don't put this bloody restriction on voidal mages.