Yep, cyanide and arsenic are also all natural. But I wouldn't administer them to my animal
Stick with Ryle's advice here, this is a management issue but you do need to get ulcers healing as well and for that I'd go with something that has been tested and proven safe, not something that people claim to be safe by word of mouth. If there really were such "miracle cures" for horses with gastric ulcers, which is one of the leading health problems in horses, it wouldn't be super cheap. Part of the reason that effective medical treatments are expensive is because they take a lot of testing and development to make sure that they are safe for our animals. For me, I'm willing to spend the extra money to be sure I'm not causing more harm than good.
Also, Pepto is a human product. I wouldn't give it to a horse and it can be fatal in dogs and cats, just an FYI.