Why is selling fake medicine legal in the USA?

https://www.tiktok.com/t/ZTFxS8UeJ/

This user appears on my TikTok feed all the time selling some product that she claims helps with acid reflux. As someone who has acid reflux, I have done a massive amount of research, and even read research papers and research studies on the subject to aid in my treatment of the illness. It's a pretty serious illness, and it's definitely not easy to treat or come up with a treatment plan, which is why there are so few medicines that are actually FDA approved for it...

But this lady is out here pushing her medicine claiming it's a miracle cure to acid reflux. There are lots of these nowadays, not only on TikTok but on Facebook as well. People pushing these alternative treatments and making such ridiculous claims, half of them probably false.

What I want to know is this. Why is this legal in the USA? Surely there should be some sort of governing body that prevents people from doing this and makes it illegal to spread this kind of misinformation?