The answer your looking for is most likely GTP. Opioid receptors are g coupled protein receptors (GCPR) which. Understanding this mechanism requires a basic understanding of biochemistry and the central dogma of molecular biology. But you can think of GTP as a molecule that does work. So the opioid binds, causes a change on the other end of the protein receptor, which leads to downstream effects and ends when GDP is replaced by GTP, causing a conformational change in the GPCR, releasing the opioid.