Nayeban 2014.

Methods	RCT
Participants	90 participants randomised Included: participants within the age range of 18 to 26 years, single, with regular menstruation, no urogenital and coagulation disorders, and no previous history of abdominal or pelvic surgery Excluded: participants whose mean score of pain severity was < 40 (based on VAS) Age: mean = 29.7 years Source: students in the dormitories of Ferdowsi University of Mashhad Location: Iran
Interventions	Group 1: vitamin B1 100 mg/day (since the 15th day of the menstrual cycle until the beginning of the next cycle) Group 2: vitamin E 400 units/day (5 days in a month, from 2 days before the menstruation until the first 3 days) The treatment course continued for 3 menstrual cycles, and then the study authors collected all forms
Outcomes	Pain severity (VAS scale 10 cm); pain duration (Cox Menstrual Symptom Scale (CMSS), score 0: no pain; score 1: ≤ 0 to 5 hours of pain; score 2: 0.5 to 1 hour of pain; score 3: > 1 hour of pain; score 4: > 1 day of pain). The study authors asked participants to record their most severe pain and its duration in the first 3 days, based on VAS and CMSS, respectively. They also asked participants if they had taken any analgesics for their pain; if so, the name and dosage of the medication was recorded in the treatment form.
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	“The participants whose mean score of pain severity was less than 40 (based on VAS), were excluded from the study, and the rest were randomly assigned to two groups.” Comment: the study authors did not describe the methods of sequence generation.
Allocation concealment (selection bias)	Unclear risk	“Each medication package was placed on a separate box, coded by letters A and B, and was given to each participant.” Comment: the study authors did not describe the method of allocation concealment in sufficient detail.
Blinding (performance bias and detection bias) All outcomes	High risk	“Each medication package was placed on a separate box, coded by letters A and B, and was given to each participant.” Comment: it is unclear whether or not the medication appearance in both groups was the same in all aspects, and also whether there was a difference of administrator.
Incomplete outcome data (attrition bias) All outcomes	Unclear risk	Comment: the study authors did not state how many participants they included in the analyses.
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.