Thapsic acid (hexadecanedioic acid) is a naturally occurring dicarboxylic acid with the formula C<sub>16</sub>H<sub>30</sub>O<sub>4</sub>. The name is derived from Thapsia, the Latin name for a Mediterranean perennial whose roots contain thapsic acid.
It has a role as a human metabolite. It is the conjugate acid of hexadecanedioate.