Table 2. Characteristics, main results and quality of evidence of the systematic reviews included.

Intervention	Comparison	Main findings	Evidence certainty (GRADE)*
Acupuncture	Acupuncture versus sham	No difference • Symptom severity • Quality of life	Moderate Moderate
	Acupuncture versus pharmacological treatment	Benefits • Proportion of participants with symptom improvement	Moderate
Antispasmodic drugs	Antispasmodic drugs versus placebo	Benefits • Improvement of abdominal pain • Overall assessment • Symptom score	NA NA NA
Antidepressants	Antidepressants versus placebo	Benefits • Improvement of abdominal pain • Overall assessment • Symptom score	NA NA NA
Bulking agents	Bulking agents versus placebo	No difference • Improvement of abdominal pain • Overall assessment • Symptom score	NA NA NA
Herbal medicines	Standard Chinese herbal formulation versusplacebo	Benefits • Overall symptom improvement • Bowel symptom scale, as rated by gastroenterologist	NA NA
		No difference • Bowel symptom scale, as rated by participant	NA
	Individualized herbal formulation versus placebo	No difference Overall symptom improvement Bowel symptom scale	NA NA
	Herbal medicines versus conventional therapy	65 RCTs assessed 51 different herbal medicines. Data were very heterogenous and not pooled**	NA
	Herbal medicines plus conventional therapy versusconventional therapy alone	9 RCTs assessed herbal medicine in combination with conventional therapy versus conventional therapy alone. Data were very heterogenous and not pooled**	NA
Homeopathy	Asafoetida versusplacebo	Benefits • Self-reported overall improvement	Very low
	Asafoetida associated with nux versusplacebo	No difference • Self-reported overall improvement	Very low
	Homeopathic consultation plus target treatment versus usual care	No difference • Wellbeing outcome	NA
Hypnotherapy	Hypnotherapy versuswaiting list	Benefits • Composite primary symptom reduction score • Proportions of hard/watery bowel movements No difference • Frequency of bowel motions (12 months) • Proportion of subjects with bloating • Frequencies of bowel motion and abdominal pain	NA NA NA NA NA
	Hypnotherapy plus pharmacological treatment versus pharmacological treatment alone.	Benefits • Abdominal pain (3 months) • Composite primary IBS symptom No difference • Quality of life (12 months) • Constipation score (3 and 12 months) • Diarrhea score (3 and 12 months) • Overall symptom score (12 months) • Abdominal pain (12 months)	NA NA NA NA NA NA NA
	Hypnotherapy versus psychotherapy plus placebo	Benefits • Abdominal pain • Bowel habit • Abdominal distension • General wellbeing	NA NA NA NA
Psychological interventions	Psychological interventions as a groupversususual care	Benefits • Symptom score improvement (2 and 3 months) • Abdominal pain improvement (2 and 3 months) • Quality of life (2 months) No difference • Quality of life (3 months)	NA NA NA NA
	Psychological interventions as a groupversusplacebo	Benefits • Symptom score improvement (2 months) No difference • Symptom score improvement (3 months) • Abdominal pain improvement (3 months)	NA NA NA
	Cognitive behavioral therapy versususual care	Benefits • Symptom score improvement (3 months) • Quality of life (2 and 3 months) No difference • Symptom score improvement (2 months) • Abdominal pain improvement (2 and 3 months)	NA NA NA NA
	Cognitive behavioral therapy versusplacebo	No difference • Symptom score improvement (2 and 3 months) • Abdominal pain improvement (2 and 3 months) • Quality of life (3 months)	NA NA NA
	Interpersonal psychotherapy versususual care	Benefits • Relief of symptoms No difference • Symptom score improvement	NA NA
	Relaxation/stress management versususual care	Benefits • Symptom score improvement (2 months) No difference • Abdominal pain improvement	NA NA

*GRADE (Grading of Recommendations Assessment, Development and Evaluation) has the aim of assessing the certainty of the body of evidence. From this, the outcomes are classified as having high certainty (high confidence that the estimated effect is close to the true effect); moderate certainty (likely that the estimated effect is close to the real effect, but there is a possibility that it is not); low certainty (limited confidence in the effect estimate) or very low certainty (the true effect is likely to be substantially different from the estimate effect). **For further information about specific types of herbal therapy, refer to the relevant text in the “Results” section of this paper. IBS = irritable bowel syndrome; NA = not assessed; RCTs = randomized clinical trials.