<unk>  <unk> , brand name Relistor), used in form of<unk>  bromide (INN, USAN, BAN), is a medication that acts as a peripherally acting μ-opioid receptor antagonist that acts to reverse some of the side effects of opioid drugs such as constipation without significantly affecting pain relief or precipitating withdrawals. Because<unk>  is a quaternary ammonium cation, it cannot cross the blood–brain barrier, and so has antagonist effects throughout the body, counteracting effects such as itching and constipation, but without affecting opioid effects in the brain such as pain relief. However, since a significant fraction (up to 60%) of opioid analgesia can be mediated by opioid receptors on peripheral sensory neurons, particularly in inflammatory conditions such as arthritis, traumatic or surgical pain,<unk>  may increase pain under such circumstances.
Methylnaltrexone
Dezocine
Bretylium
Butriptyline
Prucalopride
Desomorphine
Naltrexone
Dimethazan