If you were prescribed Erase, rather than M+ it is likely because you have never used a hydroquinone-tretinoin combination product before; have an allergy to one of the M+ ingredients; or have sensitive skin. In addition, Erase may have been better for your skin condition or if you wanted a product to treat your entire face.
Please note that once your prescription is signed by your dermatologist (at the time you receive this message) it is not recommended that it be changed until 6-8 weeks. Then, if you have used your treatment for that time period and want to try something different, you can request a prescription change, subject to your dermatologist’s approval.