Over the last few years I've always taken out a prescriptions pre-payment certificate, but this year I'm not sure whether it's worthwhile. Because I haven't paid over the counter each time I pick something up, there are some things that I don't know how they are charged. For example, asthma inhalers. Are you charged per item or per medication? If I'm prescribed 2 inhalers of the same medication, would I be charged £9.15 or £18.30?