Ref (type)	Population	Outcome, Interventions	Results and statistical analysis	Effect size	Favours
Adverse effects
Systematic review	92 people 2 RCTs in this analysis	Proportion of people with leukopenia 6 months 16/47 (34%) with interferon plus ribavirin 3/45 (7%) with interferon alone	RR 4.32 95% CI 1.56 to 11.90 P = 0.005 The review included RCTs in treatment-naïve people and people treated after relapse, and did not analyse adverse effects in people treated after non-response separately (see further information on studies for additional information on adverse effects)	Moderate effect size	interferon alone
Systematic review	7819 people 44 RCTs in this analysis	Proportion of people who discontinued treatment 6 months 645/4425 (15%) with interferon plus ribavirin 388/3394 (11%) with interferon alone	RR 1.15 95% CI 1.03 to 1.29 The review included RCTs in treatment-naïve people and people treated after relapse, and did not analyse adverse effects in people treated after non-response separately (see further information on studies for additional information on adverse effects)	Small effect size	interferon alone
Systematic review	1760 people 7 RCTs in this analysis	Proportion of people with neutropenia 6 months 59/1143 (5%) with interferon plus ribavirin 17/617 (3%) with interferon alone	RR 1.67 95% CI 1.00 to 2.77 P = 0.05 The review included RCTs in treatment-naïve people and people treated after relapse, and did not analyse adverse effects in people treated after non-response separately (see further information on studies for additional information on adverse effects)		Not significant
Systematic review	973 people 4 RCTs in this analysis	Proportion of people with thrombocytopenia 6 months 8/605 (1.3%) with interferon plus ribavirin 7/368 (1.9%) with interferon alone	RR 0.86 95% CI 0.33 to 2.22 P = 0.8 The review included RCTs in treatment-naïve people and people treated after relapse, and did not analyse adverse effects in people treated after non-response separately (see further information on studies for additional information on adverse effects)		Not significant
Systematic review	802 people 2 RCTs in this analysis	Proportion of people with dermatitis 6 months 98/512 (19%) with interferon plus ribavirin 29/290 (11%) with interferon alone	RR 1.64 95% CI 1.12 to 2.40 P = 0.01 The review included RCTs in treatment-naïve people and people treated after relapse, and did not analyse adverse effects in people treated after non-response separately (see further information on studies for additional information on adverse effects)	Small effect size	interferon alone
Systematic review	914 people Data from 1 RCT	Proportion of people with dry skin 6 months 52/456 (11%) with interferon plus ribavirin 27/458 (6%) with interferon alone	RR 1.93 95% CI 1.23 to 3.09 P = 0.004 The review included RCTs in treatment-naïve people and people treated after relapse, and did not analyse adverse effects in people treated after non-response separately (see further information on studies for additional information on adverse effects)	Small effect size	interferon alone
Systematic review	3454 people 14 RCTs in this analysis	Proportion of people with pruritus 6 months 342/1989 (17%) with interferon plus ribavirin 128/1465 (9%) with interferon alone	RR 1.82 95% CI 1.51 to 2.19 P <0.00001 The review included RCTs in treatment-naïve people and people treated after relapse, and did not analyse adverse effects in people treated after non-response separately (see further information on studies for additional information on adverse effects)	Small effect size	interferon alone
Systematic review	2064 people 8 RCTs in this analysis	Proportion of people with rash 6 months 155/1032 (15%) with interferon plus ribavirin 64/1032 (6%) with interferon alone	RR 2.39 95% CI 1.83 to 3.14 P <0.00001 The review included RCTs in treatment-naïve people and people treated after relapse, and did not analyse adverse effects in people treated after non-response separately (see further information on studies for additional information on adverse effects)	Moderate effect size	interferon alone
Systematic review	5611 people 33 RCTs in this analysis	Proportion of people who required a dose reduction 6 months 372/3135 (12%) with interferon plus ribavirin 132/2476 (5%) with interferon alone	RR 2.25 95% CI 1.89 to 2.68 The review included RCTs in treatment-naïve people and people treated after relapse, and did not analyse adverse effects in people treated after non-response separately (see further information on studies for additional information on adverse effects)	Moderate effect size	interferon alone
Systematic review	7819 people 44 RCTs in this analysis	Proportion of people who discontinued treatment 6 months 645/4425 (15%) with interferon plus ribavirin 388/3394 (11%) with interferon alone	RR 1.15 95% CI 1.03 to 1.29 The review included RCTs in treatment-naïve people and people treated after relapse, and did not analyse adverse effects in people treated after non-response separately (see further information on studies for additional information on adverse effects)	Small effect size	interferon alone