Ryetalyn

From Memory Alpha, the free Star Trek reference.

Ryetalyn is the only known antidote to the deadly disease Rigelian fever. It is a rather rare mineral.

In 2269, the crew of Federation starship USS Enterprise became infected with Rigelian fever and visited the planet Holberg 917G, which had rich natural ryetalyn deposits. There they encountered the immortal Flint and his android partner Rayna Kapec. (TOS: "Requiem for Methuselah").