Moslemi 2012.

Methods	RCT
Participants	Included: female medical students with regular menstrual cycles at the Sari Branch of Azad University who suffered, based on multi‐dimensional speech criteria, from mild or acute dysmenorrhoea Excluded: any known disease, signs of vaginal infection, history of pelvic inflammatory disease, myoma or tumour, drug or plant allergies, stressful incidence (parental divorce, or relative deaths) in the past 6 months or during the treatment Age: mean of fennel group = 25.05 years, vitamin E group = 23.25 years, and placebo group = 25.9 years Source: the Sari Branch of Azad University students Location: Iran
Interventions	Group 1: fennel extract (46 mg of hydro‐alcoholic fennel fruit extract mixed with starch) (N = 25, 22 analysed) Group 2: vitamin E (the 100‐unit vitamin E capsules) (N = 25, 20 analysed) Group 3: placebo (N = 25, 21 analysed) Participants took the pills every 6 hours for 3 days after their menstruation started for 2 consecutive menstrual cycles. (Total daily dose: vitamin E: 400 mg; fennel: 184 mg (each tablet contain 46 mg)
Outcomes	Intensity of dysmenorrhoea (multi‐dimensional speech criteria 0 to 4 scale; 0 = no pain, 3 = severe pain).
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	"Each student was placed randomly in one of three groups – vitamin E, fennel extract or placebo (each group consisted of 25 individuals) – by means of 1:1: 1 randomness and the table of random numbers."
Allocation concealment (selection bias)	Unclear risk	"The 100‐unit vitamin E capsules were purchased from local drugstores, and fennel extract capsules called Fenalgin and placebos with completely identical appearances and special coding for researchers were provided by Barij Essence Pharmaceutical Company." Comment: the study authors provided insufficient information regarding the allocation concealment method.
Blinding (performance bias and detection bias) All outcomes	Low risk	"Drugs and placebos in exactly identical covering with codes only known to the researchers were given to the study samples."
Incomplete outcome data (attrition bias) All outcomes	High risk	"Seventy‐five female individual were selected for this study". "At the end, individuals who failed to take the drugs regularly or lost one of the conditions needed to qualify for the research were removed from the study. Eventually, 63 individuals remained in the study (22 in the fennel extract group, 20 in the vitamin E group and 21 in the placebo group)." Comment: the dropout rate was 16% (12/75).
Selective reporting (reporting bias)	Unclear risk	Comment: the study authors did not prespecify adverse events as an outcome.
Other bias	Low risk	Comment: we did not identify any other potential sources of bias.