I’m not an expert on opioids but there are other factors when it comes to how long it lasts the binding strength is just one of them, the delivery method is als

I’m not an expert on opioids but there are other factors when it comes to how long it lasts the binding strength is just one of them, the delivery method is also important so are other factors such as how quickly it can pass the brain blood barrier, which other receptors it can bind too and what is the half life of the drug in vivo. Fentanyl for example can administrated with a topical patch due to its relative strength to enable longer duration of pain relief, morphine would require an injection to be as effective.