I finally got my adult acne under control using epiduo gel but now i have dark spots on my face from breaking out before. will the retin a (tretinoin) help?

Probably not.: Retin A (tretinoin) is helpful for the acne, but can actually contribute to "post-inflammatory hyper-pigmentation" ( dark spots following acne) to some degree. You can add in topical 4% hydroquinone cream as a mild bleaching agent to be used nightly on the hyper-pigmented areas to gradually lighten them up.

Actually it may.: Post inflammatory hyperpigmentation is improved with topicals that turnover the top layer of skin like all retinoids do. I like to combine Retinoic acid with lightening agents to get the most power and improvement. Beta hydroxy acid peels help a lot too.