Menstrual cramps, when due to functional problems and the release of prostaglandin F2alpha in the menstrual fluid, are a common monthly problem in menstruating women. The usual immediate treatments are anti-inflammatory drugs and prostaglandin inhibitors. One such nonsteroidal anti-inflammatory (NSAID) is mefenamic acid.
A prospective, randomized, crossover study was conducted for 2 months in 122 Iranian women aged 18-25 who had functional menstrual cramps, called primary dysmenorrhea. Group 1 received 3 peppermint oil capsules once daily for 3 days after the onset of the menses, followed by no treatment the next menstrual cycle. As best can be determined from the published study, one capsule contain 187 mg of peppermint oil. During the third menstrual cycle, these women were given 1 capsule of mefenamic acid every 8 hours for 3 days. Group 2 received these same treatments, but in reverse order: mefenamic acid cycle one, then no treatment, then peppermint oil for the third menstrual period.
Pain intensity, pain timing and bleeding amount were assessed. Both mefenamic acid and peppermint oil significantly reduced the severity of pain and there was no significant difference between the two. They also both reduced the duration of pain although mefenamic acid reduced duration more than the peppermint oil. Mefenamic acid significantly reduced bleeding, with a non-significant and slight increase with peppermint oil. Mefenamic acid did not improve nausea and vomiting, while peppermint oil significantly decreased both. Lastly, peppermint oil reduced diarrhea about four times greater than mefenamic acid.
Commentary: Peppermint contains the important active constituent, menthol, which exerts its effect on the myometrium (muscle wall of the uterus) contractions by inhibiting prostaglandin F2alpha and oxytocin. Peppermint also has analgesic and anti-inflammatory activity which explains its effect on improving vomiting and diarrhea. Drugs like mefenamic acid have potential complications such as gastrointestinal bleeding, gastrointestinal ulcers, flatulence, indigestion, stomach pain, and the worsening of colitis. While the average pain intensity and bleeding was significantly lower in the mefenamic acid group, the small difference was such that many women will gain sufficient relief with peppermint oil. I am especially familiar with using peppermint oil for the smooth muscle contractions of irritable bowel syndrome but am eager to recommend it for primary dysmenorrhea, although I will look closely at the dosages of peppermint oil products, and consider different regimens rather than the 3 capsules all at once of 187 mg per capsule, once per day during the first 3 days of the menses that was used in this study.
Reference: Masoumi S, Asi H, Poorolajal J, et al. Evaluation of mint efficacy regarding dysmenorrhea in comparison with mefenamic acid: A double blinded randomized crossover study. Iran J Nurse Midwifery Res 2016;21(4):363-367.