According to Figure 4 on page 410, it seems that 10% of ingested heroin is excreted as morphine, the other 90% as morphine glucuronides: https://www.researchga

According to Figure 4 on page 410, it seems that 10% of ingested heroin is excreted as morphine, the other 90% as morphine glucuronides: https://www.researchgate.net/profile/Wim_Van_den_Brink/publication/7196280_Population_Pharmacokinetics_of_Heroin_and_its_Major_Metabolites/links/02bfe50ec087f21de3000000.pdf https://www.researchgate.net/profile/Wim_Van_den_Brink/publi... However, it is not clear if the glucuronides would be picked up by the test. Morphine glucuronides -- particularly morphine-3-glucuronide -- can hydrolyse back to morphine. It seems that the morphine molecule is largely not destroyed metabolically; the glucuronide moiety is more like a molecular "tag" that tells the kidney to get rid of something.