Nilsson 1987.

Methods	Randomized double‐blind placebo‐controlled trial
Participants	28 patients ‐ 24 female and 4 male Average age 47.5 years Mean duration of symptoms 17.5 years
Interventions	Nifedipine 10 mg for 1 week and 20 mg (2 10‐mg capsules/d) for the next week or placebo 3×/d for 2 weeks during first treatment period, followed by 1‐week washover period Second period ‐ participants crossed over to opposite treatment
Outcomes	Changes in symptoms Side effects
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Low risk	"Randomization was made in blocks of 6."
Allocation concealment (selection bias)	Low risk	Blind allocation based on blocking
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Double‐blind cross‐over study; code broken only after conclusion of treatment
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Participant assessment of changes in symptoms and side effects
Incomplete outcome data (attrition bias) All outcomes	Low risk	1/28 (1 participant on nifedipine with dropout due to side effects)
Selective reporting (reporting bias)	Unclear risk	None detected
Other bias	Low risk	Cross‐over phases separated by 1‐week washout period