Amrits

From ENWiki

Small pearls which can be found in the oceans of Lorsul, and which are sometimes washed up on local beaches. They stop the aging of anyone who swallows them, usually for up to a year depending on the size of the pearl (though larger pearls which have been hypothesized to stop aging for five years or more are not unknown.

A pearl that stops aging for one year is worth about 500 gp on Lorsul, and 1000 gp or more on Darad.