Scorpion venom
From Tardis Wiki, the free Doctor Who reference
Scorpion venom was a poisonous substance produced by scorpions. The Tong of the Black Scorpion extracted the venom for capsules. Members were required to ingest the capsule, should their circumstances dictate it so. Ho ingested a capsule given to him by Li H'sen Chang, after he was incarcerated by police. (DW: The Talons of Weng-Chiang)