Butorphanol, nalbuphine, and pentazocine are κ agonists, with weak μ-receptor antagonist activity. Butorphanol may act as a partial agonist or antagonist at the μ receptor. Buprenorphine is a μ-receptor partial agonist with weak antagonist effects at κ and δ receptors. These characteristics can lead to decreased analgesia, or even precipitate withdrawal symptoms, when such drugs are used in patients taking conventional full μ-receptor agonists. Buprenorphine has a long duration of effect, binding strongly to μ receptors. Although prolonged activity of buprenorphine may be clinically useful (eg, to suppress withdrawal signs in dependency states), this property renders its effects resistant to naloxone reversal, since the antagonist drug has a short half-life. In overdose, respiratory depression caused by nalbuphine may also be resistant to naloxone reversal. Naloxone is included in some formulations of these agonist-antagonist drugs to discourage abuse.