BACKGROUND AND OBJECTIVE: Most of analgesics have side effects and introducing new drugs is essential. Euphorbia helioscopia is a medicinal plant which is used by people in Chaharmahal Bakhtiary province of Iran as a painkiller. This experiment was performed to study the analgesic effect of an alcoholic extract from the aerial parts of Euphorbia helioscopia by formalin test.METHODS: In an experimental study 100 Balb/c mice were divided into 10 groups as follows: group 1 received distilled

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... group 2 to 7 received 0.05, 0.1, 0.2, 0.4, 2 and 8mg/mouse of alcoholic extract, respectively. Group 8 received 6 mg/kg ibuprofen, group 9, 1 mg/kg naloxone and group 10 received naloxone and extract. The pain-related behavior was counted for a period of 30 min, following injection of 20 microliter of 1.5% formalin. The data obtained in case groups were compared with the ones in control group. The plant was extracted by maceration method using ethanol 96%. The extract was then concentrated and reconstructed in normal saline to produce different desired concentrations. FINDINGS: In the first 5 minutes (acute period) of the experiment 8mg/mouse of the extract and in the following 25 minutes, 0.1 and 8mg/mouse of the extract reduced pain reaction, compared to control group (p<0.05). Naloxone had no effect on this effect of the extract. CONCLUSION: Euphorbia helioscopia has antinociceptive activity that is not due to interaction with opioid system.