I 'm usually hopeless at remembering jokes, but I heard one the other day that stuck in the mind. A man goes to the chemist to ask for some Viagra.

"Do you have a prescription?" asks the pharmacist. "No," says the man, "will this picture of my wife do?"

It stayed with me partly because, while silly and sexist, it made me chuckle and partly because it was told to me by someone begging for spare change who offered such a quick-fire delivery of saucy jokes, he deserved every penny he got. But it mainly lodged in my brain because a few days later I had my own prescription issues to deal with (nothing to do with the little blue thrill pills).

I picked up my prescription from the busy chemist near my office one lunchtime last week, stuffed it in my bag and forgot about it until I came to take my tablets the next morning. I was about to poke one down when I realised that I'd never heard of the drug I'd been given – it wasn't what the doctor and I had talked about.

As I'd had the medicine I thought I'd been prescribed before, I knew something wasn't on. But had the doctor changed her mind about what to give me? Made a mistake? Or was it the fault of the (admittedly harried) pharmacist? Armed with Google – to work out what the hell I'd been given – and my mobile phone, I soon got to the bottom of it – the doctor was in the right, the chemist in the wrong.

But what if I hadn't known it was the wrong drug? Or I blindly assumed that what I'd been given was correct? Or, as my husband admitted he does, ignored the information leaflet and just read the label to work out how many pills to neck?

The medicine I'd been given was an antihistamine, so it's unlikely I would have keeled over, frothing at the mouth. But it could have been anything – and I'm not alone in having been handed the wrong meds.

Earlier this month, a study commissioned by the General Medical Council revealed that one in 20 prescription items were wrong in some way due to GP or pharmacy error, or because they'd been told to take the wrong dose. Over the course of a year, that means 45 million errors, with 1.6 million of them considered by the study to be "severe". People over 75 were most likely to have experienced a mistake because they tend to be prescribed more drugs.

These figures have made me realise I need to be more careful.

I will read over my prescription when I'm still with the doctor, pick a quieter chemist, double check what the pharmacist's given me and read the leaflet like a hawk. I might have been too busy to do this last week, but with doctors and chemist staff also working flat out, I'll make sure I make time for it in future.

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