Even though homeopathic remedies ARE made from natural substances–plants, minerals, animals, etc.–they are qualitatively different from vitamins and supplements. You could think of homeopathic remedies as super-concentrates, or essences. Because they are much more powerful than their “crude” origins, they are classified as medicines, and thus need to be used much more carefully. For example, if you are self-treating, don’t repeat a remedy for more than 3 days. If it hasn’t helped you by then, it isn’t going to!
Another difference in using herbs vs using a homeopathic remedy is that, while herbs might be used to address individual symptoms–e.g., a runny nose or constipation–homeopathic remedies are designed to treat the whole person, taking into account not only all physical symptoms, but emotional and mental issues as well. This whole-system aspect also means that the correct homeopathic remedy for any given person is much more difficult to find.