I am sensitive to histamine, but have to take opioids for pain. which opioid releases the least histamine?

Depends. : Each person is different. You can take Benadryl (diphenhydramine) to help. But be careful as it can also make you a lot more drowsy. If your using opioids frequently, please see your doctor...dependence can occur quickly without you even realizing it.

Opioid combo: All opioids achieve their analgesic effect by reducing or inhibiting nociceptive transmission through preventing the release of the excitatory neurotransmitters. All of them induce histamine release. If concerned, look for some opioid and antihistamine (benadryl) combination product. Talk to your PCP for more information.