Investigators in Israel conducted a prospective, observational, open-label study of isotretinoin in 638 patients with moderate acne. Patients were divided into two groups. Group 1 contained 495 patients aged 12 to 20 years with a 2:1 female:male ratio. Group 2 contained 122 patients aged 21 to 35 years with a 3.5:1 female:male ratio. All patients received 20 mg/day of isotretinoin for 6 months. Patients were evaluated every 2 months through unblinded clinical examinations and laboratory tests. Pregnancy tests were done at baseline for women with childbearing potential. Follow-up was not explicitly reported but took place over a period of up to 4 years.
A total of 617 patients completed the study. In group 1, 95% of patients achieved considerable improvement or complete remission of their acne; 26 patients (5%) did not respond and either their isotretinoin dose was increased to 30–40 mg/day, oral erythromycin was added, or the low-dose isotretinoin was continued for 8 months until remission occurred. The mean cumulative dose in group 1 was 70 mg/kg. In the follow-up period, 20 patients (4%) relapsed. Polycystic ovary syndrome was subsequently diagnosed in 7 of the patients who relapsed.
In group 2, 93% achieved significant improvement or remission, and 7% did not respond. In these nonresponders, the isotretinoin dose was either increased or continued at the low-dose level for 9 months until remission was achieved. The mean total dose was 67 mg/kg. Seven patients (6%) relapsed; of these, polycystic ovary syndrome was diagnosed in two.
The most common side effects were mild cheilitis (91%) and mild xerosis (43%). Epistaxis was reported in 2.5%. There were no pregnancies and no reported depression or other psychological side effects. A slight and transient elevation of liver enzymes (5%) and serum lipids (4%) was seen. One patient discontinued the medication due to a marked increase in triglycerides.
Here's one with a bigger sample size.. Again, these are doses of 2-4x what I'd recommend starting at. Most people can see great improvement in the 10-20 mg range.