There are poisons available for all three physical attributes, but not any for mental ones. I'd suggest a WIS damage poison, called Mist Tincture, that operates as the normal vials do, but with a "self inflict" power too.
Mist Tincture (Mild/Weak/Average/Strong)
"This small vial of liquid contains refined Mist Essence dissolved in oil. If injected, or introduced into a wound, it induces violent and reputedly prophetic hallucinations. It has gained a certain notoriety in various circles. Hunters, prophets, Docks junkies, and assassins." Poison weapon 1 use. DC depending on poison strength.
Item's special Power (consumable tainted with Chaos Mist or other WIS poison) Single Use
Average to Strong variants off Mist Ogres and Wild Orcs.
Weak/Mild variants from the Dreamers/drug dealer?
Reasons supporting:
- Of the three mental attributes, WIS is the one that's relied on by four classes with good FORT saves (Monk, Cleric, Druid, Ranger). Decent CHA or INT poisons would be overpowering as they'd target three classes with low FORT, but WIS damage would be reasonably balanced.
- The RP value of a single-target Mist-based drug (as opposed to Mist Essence that's class restricted and AOE) that could be RPed as being used deliberately, or malevolently. Deliberately, by using the power. Malevolently by say, shooting a Mist-venomed dart at a victim so they become confused in the middle of a speech.
Well you're right that contact poison for Int/Wis/Cha seems to be lacking. I think it would be a fine idea to allow for something like this, perhaps to be a little more expensive because its effects are a little more subtle and powerful against casters.
My assumption is they're lacking because INT and CHA poisons would be very, very strong indeed. Wizards and Sorcs have crappy Fortitude and 90% rely entirely on their spells for both offense and defense, so damaging a primary stat would wreck a PC. On the other hand, every class that relies on Wisdom has reasonable AB and doesn't rely on direct offensive spells as much as they do attacks. They also have additional non-spell abilities and good saves against poisons. Finally, Wisdom Damage would be an interesting thing to inflict on PCs or tough mobs in order to set them up for a will-save spell from an ally.