Examples of plants used as medicine

Few herbal remedies have conclusively demonstrated any positive effect on humans, possibly due to inadequate testing. Many of the studies cited refer to animal model investigations or in-vitro assays and therefore cannot provide more than weak supportive evidence.

• Aloe vera has traditionally been used for the healing of burns and wounds. A systematic review (from 1999) states that the efficacy of aloe vera in promoting wound healing is unclear, while a later review (from 2007) concludes that the cumulative evidence supports the use of aloe vera for the healing of first to second degree burns.
• Agaricus blazei mushrooms may prevent some types of cancer.
• Artichoke (Cynara cardunculus) may reduce production cholesterol levels according to in vitro studies and a small clinical study.
• Blackberry (Rubus fruticosus) leaf has drawn the attention of the cosmetology community because it interferes with the metalloproteinases that contribute to skin wrinkling.
• Black raspberry (Rubus occidentalis) may have a role in preventing oral cancer.
• Boophone (Boophone disticha) This highly toxic plant has been used in South African traditional medicine for treatment of mental illness . Research demonstrate in vitro and in vivo effect against depression.
• Butterbur (Petasites hybridus)
• Calendula (Calendula officinalis) has been used traditionally for abdominal cramps and constipation. In animal research an aqueous-ethanol extract of Calendula officinalis flowers was shown to have both spasmolytic and spasmogenic effects, thus providing a scientific rationale for this traditional use. There is "limited evidence" that calendula cream or ointment is effective in treating radiation dermatitis.
• Cranberry (Vaccinium oxycoccos) may be effective in treating urinary tract infections in women with recurrent symptoms.
• Echinacea (Echinacea angustifolia, Echinacea pallida, Echinacea purpurea) extracts may limit the length and severity of rhinovirus colds; however, the appropriate dosage levels, which might be higher than is available over-the-counter, require further research.
• (Sambucus nigra) may speed the recovery from type A and B influenza.However it is possibly risky in the case of avian influenza because the immunostimulatory effects may aggravate the cytokine cascade.
• Feverfew (Chrysanthemum parthenium) is sometimes used to treat migraine headaches. Although many reviews of Feverfew studies show no or unclear efficacy, a more recent RTC showed favorable results Feverfew is not recommended for pregnant women as it may be dangerous to the fetus.
• Gawo (Faidherbia albida), a traditional herbal medicine in West Africa, has shown promise in animal tests
• Garlic (Allium sativum) may lower total cholesterol levels
• German Chamomile (Matricaria chamomilla) has demonstrated antispasmodic, anxiolytic, antiinflammatory and some antimutagenic and cholesterol-lowering effects in animal research. In vitro chamomile has demonstrated moderate antimicrobial and antioxidant properties and significant antiplatelet activity, as well as preliminary results against cancer. Essential oil of chamomile was shown to be a promising antiviral agent against herpes simplex virus type 2 (HSV-2) in vitro.
• Ginger (Zingiber officinale), administered in 250 mg capsules for four days, effectively decreased nausea and vomiting of pregnancy in a human clinical trial.
• Grapefruit (Naringenin) components may prevent obesity.
• Green tea (Camelia sinensis) components may inhibit growth of breast cancer cells and may heal scars faster.
• Purified extracts of the seeds of Hibiscus sabdariffa may have some antihypertensive, antifungal and antibacterial effect. Toxicity tested low except for an isolated case of damage to the testes of a rat after prolonged and excessive consumption.
• Honey may reduce cholesterol. May be useful in wound healing.
• Lemon grass (Cymbopogon citratus), administered daily as an aqueous extract of the fresh leaf, has lowered total cholesterol and fasting plasma glucose levels in rats, as well as increasing HDL cholesterol levels. Lemon grass administration had no effect on triglyceride levels.
• Magnolia
• Meadowsweet (Filipendula ulmaria, Spiraea ulmaria) can be used for a variety of anti-inflamatory and antimicrobial purposes due to presence of salicylic acid. Effective for fevers and inflammations, pain relief, ulcers and bacteriostatic. Listed as therapeutical in 1652 by Nicholas Culpeper. In 1838, salicylic acid was isolated from the plant. The word Aspirin is derived from spirin, based on Meadowsweet's synonym name Spiraea ulmaria.
• Milk thistle (Silybum marianum) extracts have been recognized for many centuries as "liver tonics." Research suggests that milk thistle extracts both prevent and repair damage to the liver from toxic chemicals and medications.
• Nigella sativa (Black cumin) has demonstrated analgesic properties in mice. The mechanism for this effect, however, is unclear. In vitro studies support antibacterial, antifungal, anticancer, anti-inflammatory and immune modulating effects. However few randomized double blind studies have been published.
• Ocimum gratissimum and tea tree oil can be used to treat acne.
• (Origanum vulgare) may be effective against multi-drug resistant bacteria.
• Pawpaw can be used as insecticide (killing lice, worms).
• Peppermint oil may have benefits for individuals with irritable bowel syndrome.
• Phytolacca or Pokeweed can be applied topically or taken internally. Topical treatments have been used for acne and other ailments. It is used as a treatment for tonsilitis, swollen glands and weight loss.
• Pomegranate contains the highest percentage of ellagitannins of any commonly consumed juice. Punicalagin, an ellagitannin unique to pomegranate, is the highest molecular weight polyphenol known. Ellagitannins are metabolized into urolithins by gut flora, and have been shown to inhibit cancer cell growth in mice. Rauvolfia Serpentina, high risk of toxicity if improperly used extensively in India for sleeplessness, anxiety, and high blood pressure.
• (Aspalathus linearis) contains a number of phenolic compounds, including flavanols, flavones, flavanones, flavonols, and dihydrochalcones. Rooibos has traditionally been used for skin ailments, allergies, asthma and colic in infants. In an animal study with diabetic mice, aspalathin, a rooibos constituent improved glucose homeostasis by stimulating insulin secretion in pancreatic beta cells and glucose uptake in muscle tissue.
• Rose hips – Small scale studies indicate that hips from Rosa canina may provide benefits in the treatment of osteoarthritis. Rose hips show anti COX activity. Salvia lavandulaefolia may improve memory
• Saw Palmetto can be used for BPH. Supported in some studies, failed to confirm in others.^[
• Shiitake mushrooms (Lentinus edodes) are edible mushrooms that have been reported to have health benefits, including cancer-preventing properties. In laboratory research a shiitake extract has inhibited the growth of tumor cells through induction of apoptosis. Both a water extract and fresh juice of shiitake have demonstrated antimicrobial activity against pathogenic bacteria and fungi in vitro.
• Soy and other plants that contain phytoestrogens (plant molecules with estrogen activity) (black cohosh probably has serotonin activity) have some benefits for treatment of symptoms resulting from menopause.
• St. John's wort, has yielded positive results, proving more effective than a placebo for the treatment of mild to moderate depression in some clinical trials^. A subsequent, large, controlled trial, however, found St. John's wort to be no better than a placebo in treating depression^. However, more recent trials have shown positive results or positive trends that failed significance. A 2004 meta-analysis concluded that the positive results can be explained by publication bias but later analyses have been more favorable. The Cochrane Database cautions that the data on St. John's wort for depression are conflicting and ambiguous.
• Stinging nettle In some clinical studies effective for enign prostatic hyperplasia and the pain associated with osteoarthritis. In-vitro tests show antiinflammatory action. In a rodent model, stinging nettle reduced LDL cholesterol and total cholesterol. In another rodent study it reduced platelet aggregation.
• Valerian root can be used to treat insomnia. Clinical studies show mixed results and researchers note that many trials are of poor quality.Willow bark (Salix alba) can be used for a variety of anti-inflamatory and antimicrobial purposes due to presence of salicylic acid and tannins. Has been in use for aprox. 6000yrs and was described in the 1st century AD by Dioscorides.

Safety

For partial list of herbs with known adverse effects, see List of herbs with known adverse effects.

The safety and effectiveness of alternative medicines have not been scientifically proven and remain largely unknown. A number of herbs are thought to be likely to cause adverse effects Furthermore, "adulteration, inappropriate formulation, or lack of understanding of plant and drug interactions have led to adverse reactions that are sometimes life threatening or lethal." Proper double-blind clinical trials are needed to determine the safety and efficacy of each plant before they can be recommended for medical use. Although many consumers believe that herbal medicines are safe because they are "natural", herbal medicines and synthetic drugs may interact, causing toxicity to the patient. Herbal remedies can also be dangerously contaminated, and herbal medicines without established efficacy, may be used to replace medicines that do have corroborated efficacy.

Standardization of purity and dosage is not mandated in the United States, but even products made to the same specification may differ as a result of biochemical variations within a species of plant. Plants have chemical defense mechanisms against predators that can have adverse or lethal effects on humans. Examples of highly toxic herbs include poison hemlock and nightshade. They are not marketed to the public as herbs, because the risks are well known, partly due to a long and colorful history in Europe, associated with "sorcery", "magic" and intrigue. Although not frequent, adverse reactions have been reported for herbs in widespread use. On occasion serious untoward outcomes have been linked to herb consumption. A case of major potassium depletion has been attributed to chronic licorice ingestion, and consequently professional herbalists avoid the use of licorice where they recognise that this may be a risk. Black cohosh has been implicated in a case of liver failure. Few studies are available on the safety of herbs for pregnant women, and one study found that use of complementary and alternative medicines are associated with a 30% lower ongoing pregnancy and live birth rate during fertility treatment. Examples of herbal treatments with likely cause-effect relationships with adverse events include aconite, which is often a legally restricted herb, ayurvedic remedies, broom, chaparral, chinese herb mixtures, comfrey, herbs containing certain flavonoids, germander, guar gum, liquorice root, and pennyroyal. Examples of herbs where a high degree of confidence of a risk long term adverse effects can be asserted include ginseng, which is unpopular among herbalists for this reason, the endangered herb goldenseal, milk thistle, senna, against which herbalists generally advise and rarely use, aloe vera juice, buckthorn bark and berry, cascara sagrada bark, saw palmetto, valerian, kava, which is banned in the European Union, St. John's wort, Khat, Betel nut, the restricted herb Ephedra, and Guarana.

There is also concern with respect to the numerous well-established interactions of herbs and drugs. In consultation with a physician, usage of herbal remedies should be clarified, as some herbal remedies have the potential to cause adverse drug interactions when used in combination with various prescription and over-the-counter pharmaceuticals, just as a patient should inform a herbalist of their consumption of orthodox prescription and other medication.

Dangerously low blood pressure may result from the combination of an herbal remedy that lowers blood pressure together with prescription medicine that has the same effect. Some herbs may amplify the effects of anticoagulants. Certain herbs as well as common fruit interfere with cytochrome P450, an enzyme critical to much drug metabolism.

Effectiveness

Running total of the number of research papers listed on PubMed from 1990-2007 containing the word "phytotherapy."

The gold standard for pharmaceutical testing is repeated, large-scale, randomized, double-blind tests. Some plant products or pharmaceutical drugs derived from them are incorporated into medicine. To recoup the considerable costs of testing to the regulatory standards, the substances are patented and marketed by pharmaceutical companies.^[191]

Many herbs have shown positive results in-vitro, animal model or small-scale clinical tests but many studies on herbal treatments have also found negative results. The quality of the trials on herbal remedies is highly variable and many trials of herbal treatments have been found to be of poor quality, with many trials lacking an intention to treat analysis or a comment on whether blinding was successful. The few randomized, double-blind tests that receive attention in medical publications are often questioned on methodological grounds or interpretation. Likewise, studies published in peer-reviewed medical journals such as Journal of the American Medical Association receive more consideration than those published in specialized herbal journals.

One study found that non-impact factor alternative medicine journals published more studies with positive results than negative results and that trials finding positive results were of lower quality than trials finding negative results. High impact factor mainstream medical journals, on the other hand, published equal numbers of trials with positive and negative results. In high impact journals, trials finding positive results were also found to have lower quality scores than trials finding negative results. Another study reported that some clinical studies of herbal medicines were not inferior to similar medical studies. However, this study used a matched pair design and excluded all herbal trials that were not controlled, did not use a placebo or did not use random or quasi random assignment.

Herbalists criticize mainstream studies on the grounds that they make insufficient use of historical usage, which has been shown useful in drug discovery and development in the past and present. They maintain that tradition can guide the selection of factors such as optimal dose, species, time of harvesting and target population.

Dosage is in general an outstanding issue for herbal treatments: while most medicines are heavily tested to determine the most effective and safest dosages (especially in relation to things like body weight, drug interactions, etc.), there are fewer varieties of dosages for various herbal treatments on the market. Furthermore, from a conventional pharmacological perspective, herbal medicines taken in whole form cannot generally guarantee a consistent dosage or drug quality, since certain samples may contain more or less of a given active ingredient.

Several methods of standardization may be applied to herbs. One is the ratio of raw materials to solvent. However different specimens of even the same plant species may vary in chemical content. For this reason, thin layer chromatography is sometimes used by growers to assess the content of their products before use. Another method is standardization on a signal chemical.

Clinical studies

In 2004 the U.S. National Center for Complementary and Alternative Medicine of the National Institutes of Health began funding clinical trials into the effectiveness of herbal medicine.

Name confusion

The common names of herbs (folk taxonomy) may not reflect differences in scientific taxonomy, and the same (or a very similar) common name might group together different plant species with different effects. For example, in 1993 in Belgium, medical doctors created a formula including some Traditional Chinese medicine (TCM) herbs for weight loss. One herb (Stephania tetrandra) was swapped for another (Aristolochia fangchi) whose name in Chinese was extremely similar but which contained higher levels of a renal toxin, aristolochic acid; this mistake resulted in 105 cases of kidney damage.^[200][201] Note that neither herb used in a TCM context would be used for weight loss or given for long periods of time. For this reason, Western herbalists use binomial nomenclature in their terminology within the profession.

In Chinese medicine these herbs are used for certain forms of acute arthritis and edema.

Standards and quality control

The issue of regulation is an area of continuing controversy in the EU and USA. At one end of the spectrum, some herbalists maintain that traditional remedies have a long history of use, and do not require the level of safety testing as xenobiotics or single ingredients in an artificially concentrated form.^{[citation needed]} On the other hand, others are in favor of legally enforced quality standards, safety testing and prescription by a qualified practitioner. Some professional herbalist organizations have made statements calling for a category of regulation for herbal products. Yet others agree with the need for more quality testing but believe it can be managed through reputation without government intervention. The legal status of herbal ingredients varies by country.

In the EU, herbal medicines are now regulated under the European Directive on Traditional Herbal Medicinal Products.

In the United States, most herbal remedies are regulated as dietary supplements by the Food and Drug Administration. Manufacturers of products falling into this category are not required to prove the safety or efficacy of their product, though the FDA may withdraw a product from sale should it prove harmful.

The National Nutritional Foods Association, the industry's largest trade association, has run a program since 2002, examining the products and factory conditions of member companies, giving them the right to display the GMP (Good Manufacturing Practices) seal of approval on their products.

In the UK, herbal remedies that are bought over the counter are regulated as supplements, as in the US^{[citation needed]}. However, herbal remedies prescribed and dispensed by a qualified "Medical Herbalist", after a personal consultation, are regulated as medicines.

A Medical Herbalist can prescribe some herbs which are not available over the counter, covered by Schedule III of the Medicines Act^{[citation needed]}. Forthcoming changes to laws regulating herbal products in the UK, are intended to ensure the quality of herbal products used.

Some herbs, such as Cannabis, are outright banned in most countries. Since 2004, the sales of ephedra as an dietary supplement is prohibited in the United States by the Food and Drug Administration.^[209], and subject to Schedule III restrictions in the United Kingdom.

Danger of extinction

On January 18, 2008, the Botanic Gardens Conservation International (representing botanic gardens in 120 countries) stated that "400 medicinal plants are at risk of extinction, from over-collection and deforestation, threatening the discovery of future cures for disease." These included Yew trees (the bark is used for cancer drugs, paclitaxel); Hoodia (from Namibia, source of weight loss drugs); half of Magnolias (used as Chinese medicine for 5,000 years to fight cancer, dementia and heart disease); and Autumn crocus (for gout). The group also found that 5 billion people benefit from traditional plant-based medicine for health care. Some herbalists are aware of this problem and substitute least concern species as a result.