Alternative medicine is a really big business, and is practiced around the world (in some places more than others).
In some place in the world it might be practiced because the people there either can't afford modern medicine, or more likely they either just can't get access to modern medicine, or they feel they have no need for modern medicine because they have been taught that their local folk medicine works. In other places in the world it could be just simply that they don't trust pharmaceutical companies.
So back at the subject at hand, alternative medicine can be basically categorized into three different types:
While many people might say that no forms of alternative medicine work, there are in fact a few that do work to some extent, they just don't do to the extent that many of the practitioners of that alternative medicine claims, and that there are more effective (and sometimes cheaper) conventional medical practices that can be done.
Examples of this would be acupuncture, chiropractic therapy, and even vitamin supplements can be categorized into this group, and that is if these things done correctly, otherwise some of these things could be not effective at all, or even dangerous.
It should also be noted that this is the smallest category for alternative medicines as most alternative medical practices are like the next two categories.
This is the largest of the three alternative medicine categories as simply put, almost all alternative medical practices just do not work at all, and is mainly based off of anecdotal evidence, rather than real, scientific evidence.
Some of the (many) examples of this type of alternative medicine are Reiki therapy, crystal healing, naturopathy, certain alternative cancer and HIV treatments, and biggest of all, homeopathy.
While non-effective alternative medicine is not outright harmful, in some cases (such as with alternative cancer and HIV treatments) it is indirectly harmful because whomever is taking the "alternative treatments" and foregoing the proven, real medical treatments, is basically killing themselves.
While all forms of alternative medicine could be considered dangerous in their own ways, there are some forms of alternative medicine that really is harmful and dangerous if you use it, and can lead to permanent injuries, and even death.
Some examples of this are salt water flushes, colloidal silver (if used in excessive amounts), herd immunity, and reparative therapy have all been proven to be harmful, and in some cases, illegal (although usually if it is used on a minor, but sometimes some of these things are illegal for anyone to use).