Butorphanol in perspective.

Butorphanol tartrate is a highly effective opioid agonist-antagonist analgesic with qualitative as well as quantitative differences from the pure agonists. These differences are thought to be due to interaction with a distinct subset of opioid receptors. Although it relieves severe pain, the drug does not usually elevate mood, and it may occasionally cause dysphoria. Counterbalancing its disadvantages is a wealth of clinical experience with the drug showing an impressive record of safety. Butorphanol produces limited respiratory depression and smooth muscle spasm, and both effects are reversible with naloxone. The most prominent side effect is sedation, a property that is generally quite useful in the perioperative period. Butorphanol is a weak morphine antagonist, so it may interact with agonists like morphine or fentanyl. The chief advantages of this agent are its low toxicity and very low potential for abuse.