Herbal and alternative medicines are increasingly used, and even more increasingly recognized by patients and consumers alike. While the use of these agents is understandable, and may certainly be beneficial, there are a number of important points to be recognized by those who prescribe them. In most cases, that prescriber is YOU, and you therefore have to take at least a little time to do your prescribing as carefully as you would expect of your physician. The list of points below is rather long . . . but you really need to pay attention to all of them.

The term "natural" or "herbal" does not in any way necessarily mean "safe" (snake venom is natural . . . and deadly)
The FDA investigates medications and is also responsible for food items and additives. This federal agency demands proof of a level of effectiveness for drugs, and at least safety for food. It is very much worth remembering that herbal remedies are considered neither drug nor food, and are virtually unregulated. As opposed to drug development in which the pharmaceutical company must involve itself in expensive proofs of safety and effectiveness to the FDA, this same agency requires no proof of anything from those who sell herbs (Europeans do have controls on herbs). Indeed, the FDA would have to prove unsafety to remove them from the market. Be careful in your choice of preparations . . . there are unsafe fly-by-night vendors alongside those selling safe preparations.
When evaluating an herbal preparation, be sure the label contains information on the product's scientific name, plant parts used, name and address of the manufacturer, batch and lot number, and dates of manufacture and expiration.
The self-prescriber of multiple herbs will be experimenting with his/her own combination of therapies. This markedly increases the potential for negative interactions.
These agents do definitely have biologic effects . . . they will interact with prescription medicines and may cause other side effects. You really need to let your "conventional physician" know what you're taking.
While the name on the bottle may be a familiar one, in many cases you really don't know all of the ingredients you're getting in a particular formulation. Perhaps the best source of information on herbs is the (recently translated to English) German Commission E Monographs (almost 700 pages long). This is a useful resource. However, while valuable information is available, remember that the information was obtained in the regulated European community, and non-regulated American preparations may be different. Furthermore, the studies that were done were supervised by physicians, and did not measure the effects of the usual American practice of herbs of consumer self-prescription.
Be particularly careful if you are pregnant. Discuss all formulations with your doctor as you would any other drug.
Self-prescription of herbs involves self-diagnosis. It would be hard to gauge which could be more dangerous. Please be careful with both.
Likewise, as a self-prescriber, you are in the position of choosing your own dose. Do not be tempted to believe that "if a little bit is good, more is better". Choose reasonable doses.
It has been argued for years that "there isn't enough money" in herbs because they can't be patented for profit by the giant drug companies. There are several fallacies to this argument in the late 1990's.
1) There is now a US Government agency tasked with investigating similar agents.
2) There is "big money" in herbs, about $24 billion per year . . . surely someone could afford a few simple clinical studies to help their users make informed decisions!
3) The big drug companies like Bayer, SmithKlineBeecham and Whitehall-Robins are marketing lines of herbal remedies.
4) Finally, the most successful of the herbal remedies (saw palmetto for prostate problems) is seeking FDA approval as a bona fide drug. A slightly different formulation has been devised which does allow the manufacturer to patent the process. Look for others to follow.
I think these points allow us, consumers and physicians, to demand more studies and reliable information from the herb industry.
Many herbs have been studied to some degree, and there is evidence that they can produce biological activity in the test tube and in the body. The fact that an agent can be shown to create a measurable change which might be helpful does give impetus to further investigation. For example, many herbs claim to decrease laboratory parameters associated with blood clotting -- this does not in any way mean that it will actually work in humans in the same way. The pharmaceutical industry is well-experienced with investigating substances with similar promise that don't pan out for a variety of reasons. Don't be overly optimistic about an herb because there is a little science behind it -- careful clinical trials are necessary before there is proof that it works. There are many things that are "antioxidants" indeed, and their ingestion can be fatal. This is not trying to imply that the agents listed here would be deadly, but to point out that looking at just one aspect of a drug or herb's activity, particularly those that are shown only in a test tube, could give a very inaccurate idea of its overall effects. Finally, remember that the best method is to have multiple clinical trials showing an effect.
There are unquestionably persons promoting some substances of very questionable value. Beware, the Internet is one of their very favorite places to do business.
Like everything else, herbs do not make up for improper health practices such as lack of exercise, overweight or a poor diet.
Perhaps the biggest danger is misallocation of scarce resources. By that I mean the danger that people will place their money and their faith too much in unproven remedies. It is not unreasonable to view these agents as complementary, but beware of not doing well proven "conventional" modes of therapy. While not all chemotherapy is curative, many are . . . There are far too many stories of people turning down some of the well-proven chemotherapy regimens to follow herbal remedies which are unlikely to provide benefit.
The greatest danger of herbal therapy is that it may replace a more accurate diagnosis or more effective therapy.