Coulabine

This very fine greyish gas, once released, causes a strong acceleration of breathing in the victim(s). Any action more fatiguing than a slow march is generally impossible.
A creature subjected to this poison must succeed on a DC 13 Constitution DC 13 saving throw or be poisoned for up to 8 hours. While poisoned, the creature is considered to have level 4 exhaustion (if not superior before). Each hour, the creature can make a new saving throw. Each success reduces the level of exhaustion by 1. Once at level 0, the creature is no longer poisoned.