Is tyrostat effective for PIH?

I am currently on adapalene .01 gel in microsphere. On the 5th week, previous acne has left me with PIH but i still get some pimples now. Derm prescirbed tyrostat cream 2x a day on dark & flat blemishes. It is actually fading but im on my 4th week on it and it hasnt really cleared the blemishes completely, how long does tyrostat clear blemishes? Ive read tyrostat is a potent whitener, is it not working on my skin, why is it takinh too long to clear the PIH? Will adapalene also help with PIH?

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