Silver Point (5e Equipment)
From D&D Wiki
Price per dose: 25,000 gp
A highly, if not the most dangerous poison, harvested from rare silverthorn flowers.
A dose of silver point can only be of one poison type. When exposed to the effects of silver point, a creature must make a DC 18 Constitution saving throw or take one level of exhaustion. Every 12 seconds for 1 minute, if failed the first time, the creature must make this save again. Upon successfully saving 3 times before failing 3 times, the poison ends. upon 3 failures, the poison cannot end early, even if an antidote (DC 25 medicine check) is made. The 6th save's DC is higher, at DC 20.