Because it's not in The Constitution, the government shouldn't be regulating makers of medicine. The free market will, ultimately, act as its own regulator.In other words: if enough people are poisoned by some headache tablet or other, or drop dead, the product will fail because people don't want to poisoned or killed by their headache tablets. (I'm pretty sure people don't want to be killed, but hey - that's not what we're discussing.) The manufacturer will go out of business and future generations will be better off. The market will also try another headache tablet.
If we truly believe these Randian Marketeers, the problem won't exist because manufacturers will take care to ensure their product isn't poisonous. Just like tobacco companies ensured their product wasn't. Or asbestos companies fought to ensure their product wasn't labelled a carcinogen. Or how some British companies are quite sure the horse meat they're including in your beef is a bonus. I'm sure you get the idea.
So let's assume these Randian absolutists aren't really as callous as they claim to be. Let's say someone comes up with a free-market solution: they'll grade your headache tablets, and let you know which ones... have a lesser chance of killing the headache and not you. ... Oops?