There are different levels of poison, a poison's level dictates it's DC roll and the damage it inflicts. Poisons can be administered via: Contact, Ingestion, Inhalation and Injury.
DC rolls are always (your fortitude score)+(CON mod)+1d6
On a successful save the target takes half damage, rounded down.
1. DC 6, 1d5 damage
2. DC 8, 2d5 damage
3. DC 10, 3d5 damage
4. DC 12, 4d5 damage
5. DC 14, 5d5 damage
DC rolls are always (your fortitude score)+(CON mod)+1d6
On a successful save the target takes half damage, rounded down.
1. DC 6, 1d5 damage
2. DC 8, 2d5 damage
3. DC 10, 3d5 damage
4. DC 12, 4d5 damage
5. DC 14, 5d5 damage