The abdominal constriction response (ACR) in mice is a nociceptive reaction to intraperitoneal injection of noxious agents, characterized by waves of abdominal constriction and elongation. This response is used to assess the analgesic effects of drugs. Previous studies showed that substances like codeine, morphine, and pethidine suppressed ACR, suggesting it is a valid test for antinociception. However, this method has limitations, including ethical concerns, potential confusion with anti-inflammatory effects, and false positives. The study describes new methods for testing ACR in mice, which reduce these disadvantages. Substances like acetylcholine, bradykinin, and potassium chloride were found to induce ACR, with varying latencies. The median effective dose (ED50) for these substances was calculated, showing that acetylcholine was the most effective. Antinociceptive drugs such as morphine, cyclazocine, and aspirin were tested for their ability to suppress ACR. Morphine was consistently more potent than codeine, while aspirin showed significant potency against acetylcholine but less against other challenge substances. The study also evaluated the antinociceptive effects of various drugs, including narcotics, narcotic antagonists, and antipyretics. It found that antipyretics were more effective against acetylcholine-induced ACR than against tryptamine-induced responses. The ACR test was compared to other methods, such as the tail-clip test, and showed good correlation with human analgesic potency rankings. However, the ACR test had a higher rate of false positives, particularly with antiacetylcholine and antihistamine drugs. The study concluded that the ACR test is a useful and rapid method for initial screening of potential analgesic drugs, despite its limitations. It provides a reliable way to assess the antinociceptive effects of drugs, with results comparable to those in humans. The test is particularly effective for drugs that act peripherally, and it helps in distinguishing between narcotic and non-narcotic analgesics. However, further research is needed to refine the test and reduce false positives.The abdominal constriction response (ACR) in mice is a nociceptive reaction to intraperitoneal injection of noxious agents, characterized by waves of abdominal constriction and elongation. This response is used to assess the analgesic effects of drugs. Previous studies showed that substances like codeine, morphine, and pethidine suppressed ACR, suggesting it is a valid test for antinociception. However, this method has limitations, including ethical concerns, potential confusion with anti-inflammatory effects, and false positives. The study describes new methods for testing ACR in mice, which reduce these disadvantages. Substances like acetylcholine, bradykinin, and potassium chloride were found to induce ACR, with varying latencies. The median effective dose (ED50) for these substances was calculated, showing that acetylcholine was the most effective. Antinociceptive drugs such as morphine, cyclazocine, and aspirin were tested for their ability to suppress ACR. Morphine was consistently more potent than codeine, while aspirin showed significant potency against acetylcholine but less against other challenge substances. The study also evaluated the antinociceptive effects of various drugs, including narcotics, narcotic antagonists, and antipyretics. It found that antipyretics were more effective against acetylcholine-induced ACR than against tryptamine-induced responses. The ACR test was compared to other methods, such as the tail-clip test, and showed good correlation with human analgesic potency rankings. However, the ACR test had a higher rate of false positives, particularly with antiacetylcholine and antihistamine drugs. The study concluded that the ACR test is a useful and rapid method for initial screening of potential analgesic drugs, despite its limitations. It provides a reliable way to assess the antinociceptive effects of drugs, with results comparable to those in humans. The test is particularly effective for drugs that act peripherally, and it helps in distinguishing between narcotic and non-narcotic analgesics. However, further research is needed to refine the test and reduce false positives.