Evidence Level C
Poor quality observational (cohort) studies or methodologically flawed randomized controlled trials (RCTs) of <200 participants.
Reduction in inflammatory and non-inflammatory lesions in mild-to-moderate acne: there is poor-quality evidence that, when compared with placebo, topical tretinoin reduced the number of inflammatory and non-inflammatory lesions at 8 to 12 weeks.
More info from BMJ Clinical Evidence
