2.1. Participants
substance abuse
This study was conducted in 67 Caucasian ME/CFS patients consecutively recruited from a single outpatient tertiary referral center (ME/CFS Clinical Unit, Vall d’Hebron University Hospital, Barcelona, Spain) from September 2021 to December 2022. Exclusion criteria comprised participation in another intervention within 30 days prior to study inclusion; inability (in the opinion of the investigator) to follow the instructions or to complete the treatment satisfactorily; failure to provide signed informed consent; consumption of certain drugs/supplements that might influence outcome measures in the last 90 days or whose withdrawal might be a relevant problem, anticoagulant treatment, pregnancy or breast-feeding, smoking, alcohol intake or substance abuse, BMI ≥ 25 kg/m