How long should I take roaccutane 10/20 mg to get rid of excessive sebum? I am a 34 years old female.

I had bad cystic acne in late teens and it lasted for few years until I took roaccutane 20mg but left with excessive sebum. I restarted it few years back and have been on it on and off. The last time I did 3 months course was 2 years back. Sebum is pretty much controlled but its still there on left cheek which prevents clearing my skin from scars. It make my skin bumpy. I really want to get rid of this problem completely.

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