Composition scheme on sale of MRP products - Goods and Services Tax - GST

Dear Sir/Mam, My query is when a medical shop owner who is registered under composition scheme is selling medicines (all are B2Cs only), then whether a) He can charge MRP straight away and pay 1% GST on such MRP or; b) reduce the deemed taxes from MRP and then pay 1% GST on the net amount which is arrived after reducing the deemed taxes. This is because as MRP products are deemed to be inclusive of taxes and a composition dealer is not eligible to collect taxes.