Belpren was an acidic substance that had a luminescent blue coloring.
Although belpren was considered acidic, it was only corrosive when it came into contact with flesh or other soft tissues. It was ineffective against metal, cloth, and cured leather. The larger the area that was brought into contact with the substance, the more damage that would occur, but ingesting the poison only caused damage once. Belprin dried very quickly when exposed to air so it had to be applied immediately. It was not effective to coat it on weapons. Belpren was effective against any creature.
Belpren could be neutralized by lamp oil.
Belpren was one of sixteen formulas for poisons recorded in the book known as The Nathlum. It was thought that the formulas were originally written down by the mage Lethchauntos the Black, during his time spent with an orc tribe in the 10th century DR. Some of these same formulas were copied from the book by the mage Phrandjas of Port Llast and sold to local alchemists before the mid–14th century DR.