Challenor 1989.

Methods	Double‐blind randomized placebo‐controlled (double‐dummy) trial Cross‐over design
Participants	N = 24 patients with primary Raynaud's phenomenon ‐ 22 female, 2 male Mean age 37.7 ± 2.9 years, range 17 to 61 Mean duration of disease 21.0 ± 3.3 years 3 smokers 4 dropouts
Interventions	Continuation of concurrent treatments unchanged Patients randomized to receive nifedipine or placebo Dose increased after 3 weeks After a further 3 weeks, patients crossed over to the opposite treatment for 6 weeks, with dose increasing as before
Outcomes	Subjective and objective assessments Daily participant record of episodes, number of attacks, duration, and severity, as well as number of visits outdoors, unwanted effects, and improvement Vibration perception, skin temperature, and blood plasma measurements
Notes
Risk of bias
Bias	Authors' judgement	Support for judgement
Random sequence generation (selection bias)	Unclear risk	Evidence insufficient for judgement of risk
Allocation concealment (selection bias)	Unclear risk	Evidence insufficient for judgement of risk
Blinding of participants and personnel (performance bias) All outcomes	Low risk	Double‐dummy RCT: "Patients were randomized to receive either a 10‐mg sustained‐release formulation of nifedipine twice daily before food or a matching placebo."
Blinding of outcome assessment (detection bias) All outcomes	Low risk	Participant diary used to record episodes of Raynaud’s phenomenon, noting number of attacks, duration, and severity
Incomplete outcome data (attrition bias) All outcomes	Low risk	Two participant withdrawals from the study for personal reasons unrelated to treatment Two participant treatment discontinuations after 5 and 7 days of 40 mg sustained‐release nifedipine due to unwanted effects ‐ the latter included in the analysis
Selective reporting (reporting bias)	Low risk	No evidence of selective reporting
Other bias	Unclear risk	Evidence insufficient for judgement of risk