First I know I did not explain everything in the title. It's a little complicated.
Similar to the rules in this question.
Magic potions exist with the following rules
- Pre-industrial revolution world. It's advanced in many ways. But no more medical knowledge than that era.
- Only wizards make potions.
- Potions are plentiful.
- Potions are cheap. The poorest can afford a health potion.
- No side effects.
- Potency is a bit of an issue but not much. If you get a very deadly disease then the strongest potion will cure it. However for a strong cold or some coughing a simple or average potions is enough.
- Potions can cure all disease with the only exception being magical afflictions.
- Doctors exist to 'diagnose' cases to help people choosing the "right" potency of potion.
- The richest just jug the strongest potion.
- Wizards benefit from that system and so they are actively working towards greater integration of potions into society.
- Wizards completely control the trade with the full support of every state where those potions are available.
- Wizards take any messing around with potions as a capital offense with bloody and terrible murder as the only answer. And being wizards they can actually track and monitor just about all forms of magic.
- The state, since it's a world I'm just using this to cover all forms of government, is a part of the deal. A court wizard exists to protect and help rulers, among other things.
- Most commercially available potions are sold through licensed merchants. Those merchant are under the watchful eyes of wizards. They might be able to get their hands on unlicensed potions, but the whole system is made up in a way the makes in beneficial for all parties enveloped to follow it. And so risking getting ripped apart by demons and having your entire life savings burnt in front of your family to get a crate of potions that will get you an extra 10% of profit does not seem like a good idea to most merchants.
- There is a robust potions detection system. Again breaking it gets you killed violently.
- For all intents and purposes health potions don't degrade with time.
- Health potions are always effective. A disease can't evolve against it.
- Other forms of potions exist. For example they are given to animals, and also added to irrigation water to protect the crops.
- All sorts of potions exist with varying degrees of availability.
- Certain potions are illegal.
- Magic poisons are extra illegal.
- Using potions to aid in crimes incurs extra and sever punishments.
- Potions in general offer better than modern medicine healing while direct magic covers the rest.
- Growing limbs is usually a matter for direct magic. But limb growing potions exist, they are expensive though.
- Custom potions are possible. But scarce
Now I hope this provides enough context and answers to the rules of the most used and common potions.
However despite all this potions are illegal to use in combat. How? Again this is a part of the overall treaty between earthly powers and the ruling body of wizards.
It's illegal to use magically enhanced soldiers in fighting, it's illegal to get a wizard to inspire troops, it's illegal to call demons and control the elements to change warfare...etc
And since, so far, the wizards are a tight bunch, they don't go rogue that much. So the idea that a best asset a general or a ruler can wield is a rogue wizard is not feasible. For obvious reasons that once a thing is known, the entire state is compromised and a sort of crusade is called upon it.
The world got a lot of history with that exact sort of thing. So in this point in time those are the ruler and we should not bother with exceptions.
The last point, and sorry for thing lengthy post: Healing magic can be given to soldier after the fighting is done and they are in camp or whatever the army's healers feel appropriate. Also stamina potions are allowed. They just remove the feeling of being physically tired without enhancing a soldier. That's all I came up with, so far.
The rational is that it's basically healing people and helping them. But a potion that takes away fear and makes soldiers more violent is a hard no.
So at last:
What sort of workarounds would generals use to give themselves an advantage? But not a huge one as well, otherwise they risk wizards getting angry.
Just to make it extra super clear. The rules might be too constrictive and allow little for general to do, that's great. In that case just say so. The rules might enable a small or a big exploit for generals, again fine by me.