It probably depends what was in the meds you were buying (that's how it works in the US anyway). If it was just ibuprofen or paracetamol or something, then it's pretty harmless unless you OD-ed or something (and 15 is plenty old enough to figure out how much to take), and it's not something people get high off or anything. I don't remember if you can buy things with codeine in it over the counter in the UK, but if you can then there might be an age limit on that since it's a narcotic. We also have age limits on cough medicine with dextromethorphan in it because people take it in higher doses to get high, and also for pseudoephedrine because people use it to make methamphetamine (it also has to be kept behind the counter, and in Oregon it requires a prescription), and probably some other things that I don't ever buy. The age limits are maybe kind of counterproductive sometimes though, because I didn't even know you could get high off dextromethorphan until I looked it up online to find out why there was a sign in the pharmacy that you had to be 18 to buy it...
But, um, I'd be more concerned that you could get the alcohol to have an hangover in the first place than that you could get the painkillers to treat it
