If you have medCode in both tables, where is the problem?
The example below shows how to get records from 2 tables with equal medCodes and UnitPrices.
SELECT PM.medCode AS PM_medCode, PM.UnitPrice AS PM_UnitPrice, PM.Quantity AS PM_Quantity, NM.medcode AS NM_medcode, NM.UnitPrice AS NM_UnitPrice, NM.Quantity AS NM_Quantity
FROM Prescribed_Medicines AS PM INNER JOIN NHIS_Medicines AS NM ON PM.mdeCode = NM.medCode
ORDER BY PM.medCode
WHERE PM.UnitPrice = NM.UnitPrice