Peripheral opioid receptor agonists 

Peripheral opioid receptor agonists act on opioid receptors outside of the central nervous system, which are found in high concentrations in the bronchial smooth muscle, digestive tract, skin, and peripheral nerves. Peripheral opioid receptor agonists do not readily cross the blood-brain barrier.

The peripherally acting μ-receptor antagonists (PAMORAs) are a class of drugs that include methylnaltrexone, naloxegol, and naldemedine. Collectively, each is approved for the treatment of OIC. PAMORAs work peripherally in the gastrointestinal tract, without impacting the central analgesic effects of opioids.

Peripheral opioid receptor agonists act on opioid receptors outside of the central nervous system, which are found in high concentrations in the bronchial smooth muscle, digestive tract, skin, and peripheral nerves. Peripheral opioid receptor agonists do not readily cross the blood-brain barrier.

An agonist is a drug that activates certain receptors in the brain. Full agonist opioids activate the opioid receptors in the brain fully resulting in the full opioid effect. Examples of full agonists are heroin, oxycodone, methadone, hydrocodone, morphine, opium and others.

Opioid Agonists:
The first class includes morphine, hydromorphone, codeine, oxycodone, oxymorphone, and hydrocodone. The second class includes meperidine, fentanyl, sufentanyl, alfentanil, and remifentanyl. The third class contains methadone and propoxyphene.

Peripherally selective drugs have their primary mechanism of action outside of the central nervous system (CNS), usually because they are excluded from the CNS by the blood–brain barrier.