I guess it depends what they mean by fast-acting, eloethan. Also, charging more than what? The generic kind? No, I don't think it's misleading but I do think the intention is to grab people's attention and money, for instance the attention of someone with a migraine headache, or period pains, so they mention those on the box. That's just marketing. That's how it's done. I reckon all adults should be able to suss that companies will try to get as much money out of them as they can. My dad used to say, the cost of something is "whatever the suckers will pay". Don't read that wrongly; he was saying it bitterly. I'm not saying it's totally acceptable. I'm just saying it's reality and if the companies doing it aren't breaking the law (i.e. lying to us) there's no point whining about it.
Re your point about being able to 'trust' what it says on the box, I'm sure they would be prosecuted if they were saying anything actually untrue. We do have some standards and laws to hold marketeers to.