Chiro and acupuncture (assuming this is aprt of "alternative medicine, and S.O. else already brought it up) are borderline, not in the category of homeopathy and astrology. Most statistical studies show that, for back pain at least, chiro, physical therapy, and surgery are all about equally effective (on average they are all better than placebo, though not by very much). Chiro is based on theories that are utter horsehockey, but under our barbaric medical system in the states at least it is a way to get your medical insurance to pay for a good massage.
Acupuncture seems to work for certain types of pain, but traditional acu is no better than sham acu (pins placed at random.) In other words, there seems to be benefit in it but the elaborate traditional theories about placement of the pins and flow of chi are groundless.
Surprised to see so many people defending herbal remedies here. A few of these may work, but anything marketed as an herbal or nutritional remedy is by definition unproven. If it could be shown to be safe and effective, it would be sold at much greater profit as a drug.