If just glugging liquid hit points and bottled spells begins to feel boring, here's one way to spice it up. Thanks to Becami Cusack at Systematica for inspiration.
The potions that you find in a dungeon and were made by some freak who knows where and probably under strong influence of some underground-grown hallucinogen have 3 in 6 chance to have random side effects. Every found batch of potions shares the same side effect, including 1-potion batches.
There's also a 1 in 6 chance that the potion is actually more effective than it should've been - roll twice and pick the best result when determining its effect.
City-based alchemists sometimes make potions that have a known side effect, and sell them to common folk, lowering the price compared to basic potions - a practice made famous by an opportunistic alchemist named Generico.
The side effects start if the characters fail a saving roll versus poison when drinking the potion.
Possible side effects:
1. Allergy. The character's body itches viciously. This is annoying, and causes a -1 penalty to all rolls. What's worse, unless treated, this condition returns every time the character drinks a potion of the same type as the one that caused allergy.
2. Intoxication. Whenever the character tries to do something important, or whenever it might provide funny results, make them roll twice and pick the worse result. It's cumulative and gets worse if the character drinks more than one potion - after failing the roll versus poison twice, it's "roll thrice and pick the worst", etc. Don't apply it to the actual saving roll.
3. Bliss. The character is happy about the world and their place in it. Whenever someone - anyone - makes a suggestion, make the player roll against magic. On a failure, the character thinks the suggestion's an excellent idea, and should be implemented immediately - treat it like Suggestion spell.
4. Hallucinations. In combat, make the character roll twice and pick the worse "to hit" result, on a failure, the character strikes down a hallucinatory enemy. Out of combat, play it out as you like it.
5. Sleep. Roll to save versus magic, on a failure, treat it as a succesful Sleep spell. Reroll for elves.
6. Roll twice and combine.
I'll need to test it out but so far I like it.
If you still haven't read All Dogs Go to Hell, the latest LotFP adventure by, well, me, you can still get it at DTRPG for whatever you want to pay for it. Hurry before they run out of PDFs.