Safety and efficacy of alternative medicines and scientifically proven is largely unknown. Side effects also cause a number of herbs for the possibility, "adulteration, inappropriate formulation, or lack of understanding of drug interactions of plants and sometimes life-threatening or fatal adverse reactions that are thought path." Appropriate double-blind clinical trials can be recommended for use in the first medical safety and efficacy of each plant is required to determine. Many consumers, because "who believe that herbal medicines are safe natural", herbal remedies and synthetic drugs can interact, cause toxicity for the patient. Dangerous herbal medicines, herbal remedies are not established and effectiveness, they do have the drug can be used instead Corroborated activity may be contaminated. 
Purity standardization and dosing of the United States, but even as mandatory products plant species within the same properties as a result of a biochemical variation may be different.Plants against hunters or fatal adverse effects on humans may have chemical defense mechanisms. Examples of highly toxic herbs include poison hemlock and nightshade. Because the risks are well known herbs such as their public, partly in Europe, a long and colorful history, "magic" associated with the reasons, "magic and intrigue is not being marketed.

Although not common, widely used reaction to herbs have been reported. Vesile serious unfortunate consequences on the grass has been linked to consumption. Important potassium depletion in patients with chronic licorice ingestion is thought. And so the plant where this may be a risk to recognize the use of licorice to avoid professional. Black cohosh liver failure in a situation that has been mixed. A small number work for pregnant women herbs and security, and a study is possible complementary and alternative medicine use was 30% lower ongoing pregnancy and live birth rate and fertility during treatment are related. because of the possible treatment plant samples negative effect relationships of events specific flavonoids, hay, Guar gum, licorice root containing herbs often legally limited ot , ayurvedic medicines, cleaners, chaparral mixture of Chinese herbs, comfrey is Aconite, inclusive, and pennyroyal. Here, in the long term negative effects, so popular among the plants that Ginseng is claimed, including a high degree of risk in trust under threat goldenseal herb, Milk Thistle, senna, which generally recommended against the rare plants use herbs for example, aloe vera juice, peel and hawthorn berry, cascara Sagrada bark,,, Valerian Palmetto and Guarana, the European Union, St John's Wort, khat, betel nut, herb Ephedra limited that have been banned kava, saw . 
In addition, according to numerous well-herb and drug interactions are concerned founded.Some herbal remedies potential adverse drug interactions with various prescription and over time when used with necessary because a doctor, use of herbal medicines in consultation with,-counter drugs, just as a herbalist must notify a patient should be opening the orthodox prescriptions and other medicines for their own consumption. 
Dangerously low blood pressure has the same effect as prescription drug lowers blood pressure with a herbal drug combination may result. Effects of anticoagulants may raise some herbs.Specific cytochrome P450 as well as common fruits, herbs, a lot of obstacles critical to drug metabolism enzymes.