Girdle of Fortitude

Girdle of Fortitude is a girdle which can be used once per day to raise the constitution of the wearer to 18 for eight hours in-game. This item appears in Baldur's Gate II: Shadows of Amn and this item will probably appear in Baldur’s Gate II: Enhanced Edition. It can be found at the end of the subquest: Investigate and destroy the cult of the Unseeing. You have to kill the cult leader, Gaal, after he found out that the party killed the "deity" of the cult.

In-game description
"Girdle of Fortitude This girdle greatly increases the wearer's constitution. King Violos used it when leading an expedition against marsh trolls. He'd been severely sickened the past winter and was no longer the healthy man he once was. The belt gave extra years to his life and inspired his men to renew their confidence in their king once more."