The Drugs (Prices Control) Order is the specific piece of legislation under which scheduled formulation prices are regulated in India, and it names the National Pharmaceutical Pricing Authority as the body empowered to fix and periodically revise the ceiling prices of medicines listed in the National List of Essential Medicines. The other three bodies serve entirely different regulatory purposes: DGHS oversees public health administration, PCI regulates pharmacy education and pharmacist registration, and NMC regulates medical education and doctors, none of them are given pricing powers under the DPCO.
Therefore, the correct answer is National Pharmaceutical Pricing Authority.