10. Zinc compared to no treatment.

Zinc compared to no treatment for acne
Patient or population: participants with acne Settings: eight centres in the UK, one in France and one in Germany Intervention: topical zinc plus clindamycin 1% gel Comparison: no treatment plus clindamycin 1% gel
Outcomes	Illustrative comparative risks* (95% CI)		Relative effect (95% CI)	No. of participants (studies)	Quality of the evidence (GRADE)	Comments
	Assumed risk	Corresponding risk
	Placebo/no treatment	Topical zinc
Participants' global self‐assessment of acne improvement Visual analogue scale (long term: treatment duration > 8 weeks)	The study authors only reported no significant difference between treatment groups.			163 (1 study)	⊕⊕⊝⊝ Lowa	Clindamycin 1% gel was a co‐intervention given in both arms. No numerical data provided.
Withdrawal for any reason (long term: treatment duration > 8 weeks)	72 per 1000	87 per 1000 (31 to 249)	RR 1.21 (0.43 to 3.45)	163 (1 study)	⊕⊕⊝⊝ Lowb	Clindamycin 1% gel was a co‐intervention given in both arms.
Total number of participants who experienced at least one minor adverse event (long term: treatment duration > 8 weeks)	See comment	See comment	Not estimable	163 (1 study)	⊕⊕⊝⊝ Lowc	Clindamycin 1% gel was a co‐intervention given in both arms. The authors only report number of adverse events, not number of participants ‐ 91 adverse events in 80 zinc/clindamycin participants and 117 adverse events in 83 clindamycin participants.
Quality of life	‐	‐	‐	‐	‐	Not measured
*The basis for the assumed risk (e.g. the median control group risk across studies) is provided in footnotes. The corresponding risk (and its 95% confidence interval) is based on the assumed risk in the comparison group and the relative effect of the intervention (and its 95% CI). CI: confidence interval; RR: risk ratio.
GRADE Working Group grades of evidence High quality: further research is very unlikely to change our confidence in the estimate of effect. Moderate quality: further research is likely to have an important impact on our confidence in the estimate of effect and may change the estimate. Low quality: further research is very likely to have an important impact on our confidence in the estimate of effect and is likely to change the estimate. Very low quality: we are very uncertain about the estimate.

^aDowngraded by two levels to low quality evidence. One level for risk of bias: only one study included with high risk of performance bias and unclear risk of selection bias. One level for imprecision: small sample size.
^bDowngraded by two levels to low quality evidence. One level for risk of bias: only one study included with high risk of performance bias and unclear risk of selection bias. One level for imprecision: wide CI and optimal sample size not met.
^cDowngraded by two levels to low quality evidence. One level for risk of bias: only one study included with high risk of performance bias and unclear risk of selection bias. One level for imprecision: small sample size.
^*We choose a mean baseline risk from the studies included in meta‐analysis, calculated as number of participants in the control groups with event divided by total number of participants in control groups (study population) as assumed risk.