My asthma rescue inhaler acts immediately for relief.
I don't know the biology of it at all, clearly there are fundamental differences between how various drugs impact the body's systems. But wouldn't it be neat if everything were fast-acting? Take a decongestant and your sinuses drain out immediately. Take a sleeping pill and you are asleep exactly 30-seconds later. Take an anti-inflammatory and feel relief before the pill has even gone down. Everyday compounds would join the ranks of asthma inhalers, epinephrine pens, surgical anesthetic, etc.
I suspect most of these kinds of things would necessarily be limited to hospitals and other controller environments because instant reactions can fall between inconvenient and downright dangerous in the real world. But it's nice to dream that “magic medicine” could be more widely available.