A large number of books and websites have pages on herbal medicine. What many of them don’t tell you is that in many ways herbs can be unsafe if not used with the proper knowledge and caution.
A few facts:

Many Herbs have side effects just like medications.

Many herbs have contraindications. There are herbs that should not be used by people with certain conditions.

Many should not be mixed with other herbs or medications.

There are herbs that should be avoided during pregnancy, Some herbs can cause miscarriage or premature birth.

there are herbs that can be toxic in large doses
There are herbs that can be toxic when used over long periods of time. They can accumulate in your system and make you sick or even kill you.

You can be allergic to herbs the same as any food or medication

Before using any herb to treat an ailment, you should know the following:
Side effects, contraindications, in what doses the herb is safe, and if you are using a mixture, how much of each herb is in the dose. you can not accurately determine how much of a mixture is safe unless you know how much of each herb is in the mixture.
Natural does not always mean safe!

Finally, do not diagnose yourself. Minor ailments and serious illnesses often have similar symptoms. Always make sure you know exactly what the problem is before you attempt to treat it. Natural remedies can be great, but they do not replace qualified medical attention.

Please do not let this page put you off from using natural remedies entirely. This information was not intended to scare you. It is intended to help you use herbs safely. I am very much in favor of natural remedies, I use them regularly. But just like anything else, they must be used wisely. If in doubt, consult a doctor or herbalist.

Suggested Reading

HEALING HERBS: THE ULTIMATE GUIDE TO THE CURATIVE POWER OF NATURE'S MEDICINES by Michael Castleman