A study in Kerman, Islamic Republic of Iran in 2002 compared the effectiveness of fennel and mefenamic acid on pain relief in primary dysmenorrhoea. Two groups of high-school girls (mean age 13 years) suffering dysmenorrhoea were randomized to receive fennel extract (n = 55) or mefenamic acid (n = 55) for 2 months. In the fennel group, 80% of girls and in the mefenamic acid group, 73% of girls showed complete pain relief or pain decrease, while 80% in the fennel group and 62% in the mefenamic acid group no longer needed to rest. There was no significant difference between the 2 groups in the level of pain relief.