View source

You might at least want to add the heron metabolism is mainly first pass liver metabolism. Meaning that if you inject the stuff it doesn not have that first pass metabolism but instead crosses the blood barrier rapidly. That is described in WikiPedia but I did not check the references. If you agree I would draw two arrows from the heroin itself (or maybe form acetyl-morfin??) one annptated not just with the enzyme but also with a text saying ("first pass liver metabolism after oral uptake"). The other transporting across the blood brain barrier (annotated with "after injection rapidly passes into brain"