It is possible that it is part of his complex delusions as no one else seems to take it and nearly every bottle is labeled:
Torque. Take one bottle a day with food for delusions. Dr. Killjoy.
Nearly nothing else is known about the drug.
In-game specifics Edit
In The Suffering, Xombium can be picked up and saved for future use. However, in Ties that Bind, Xombium is used by approaching it whenever Torque's health isn't completely full.