boxtops...complete drivel I'm afraid :::
http://www.mhra.gov.uk/Safetyinformation/Medicinesinformation/SPCandPILs/?prodName=VANTAGE%20SLEEP%20AID%2050MG%20TABLETS&subsName=DIPHENHYDRAMINE%20HYDROCHLORIDE&pageID=SecondLevel
If it contains Aspirin, or Paracetamol, or anything else, and it has the same Product Licence ( PL) than it contains exactly the same ingredient, in exactly the same dosage.
EG, if you buying Paracetamol in a pack that says it is suitable for, say period pain. and it has the same PL as another, much cheaper version, that says suitable for headaches, with the same PL, you are wasting your money by buying the more expensive version. This scam has been exposed many times before, most memorably on Watchdog ::
http://www.bbc.co.uk/programmes/b006mg74/features/pain-killers
If you believe differently, then you have conned by clever marketing I'm afraid !