Scientific evidence

As a traditional medicine, many Ayurveda products have not been tested in rigorous scientific studies and clinical trials.[53] In India, research in Ayurveda is largely undertaken by the statutory body of the Central Government, the Central Council for Research in Ayurveda and Siddha (CCRAS), through a national network of research institutes.[54] A systematic review of Ayurveda treatments for rheumatoid arthritis concluded that there was insufficient evidence, as most of the trials were not done properly, and the one high-quality trial showed no benefits.[55] A review of Ayurveda and cardiovascular disease concluded that while the herbal evidence is not yet convincing, the spices are appropriate, some herbs are promising, and yoga is also a promising complementary treatment.[56]

Some ayurvedic products, mainly herbs used for phytotherapy, have been tested with promising results. Turmeric and its derivative curcumin appears to have beneficial properties.[57] Tinspora cordifolia has been tested.[58] Among the medhya rasayanas (intellect rejuvenation), two varieties of Salvia have been tested in small trials; one trial provided evidence that Salvia lavandulifolia (Spanish sage) may improve word recall in young adults,[59] and another provided evidence that Salvia officinalis (Common sage) may improve symptoms in Alzheimer's patients.[60] In some cases, Ayurvedic medicine may provide clues to therapeutic compounds. For example, derivatives of snake venom have various therapeutic properties.[61] Many plants used as rasayana (rejuvenation) medications are potent antioxidants.[62] Neem appears to have beneficial pharmacological properties.[63]
Azadirachta indica—believed to have immunopotentiating abilities and used often as an anti-infective—has been found to enhance the production of IL-2 and increase immunity in human volunteers by boosting lymphocyte and T-cell count in three weeks.[64]
Black pepper and long pepper are combined with ginger to form the traditionaltrikatu mixture in Ayurveda. This mixture increases appetite, promotes the secretion of digestive juices, and cures certain gastric disorders, particularly Achlorhydria and Hypochlorhydria.[65]

Mitra & Rangesh (2003) hold that cardamom and cinnamon stimulate digestive enzymes that break down polymeric macromolecules in the human body.[18] Research suggests that Terminalia arjuna is useful in alleviating the pain of angina pectoris and in treating heart failure and coronary artery disease.[52] Terminalia arjuna may also be useful in treating hypercholesterolemia.[52]

Major safety concerns include adulteration of herbal medicines with toxic metals, and intrinsic toxicity of herbal medications. Some traditional Ayurvedic treatments use toxic metals, herbs, and minerals as part of their remedies. Rasa Shastra, the practice of adding metals, minerals or gems to herbs, increases the likelihood of toxic metals such as lead, mercury, or arsenic in the remedy.[66] There is evidence that using some Ayurvedic medicines, especially those involving herbs, metals, minerals, or other materials involves potentially serious risks, including toxicity.[53][67] Adverse reactions to herbs due their pharmacology are described in traditional Ayurveda texts, but Ayurvedic practitioners are reluctant to admit that herbs could be toxic and the reliable information on herbal toxicity is not easily available.[68]

A 2004 study found toxic heavy metals such as lead, mercury and arsenic in 20% of Ayurvedic preparations that were made in South Asia for sale around Boston and extrapolated the data to America. It concluded that excess consumption of these products could cause health risks.[69] A 2008 study of more than 230 products found that approximately 20% of remedies (and 40% of rasa shastra medicines) purchased over the internet from both US and Indian suppliers contained lead, mercury or arsenic.[66][70][71]

Traditionally the toxicity of these materials are believed to be reduced through processes such as samskaras or shodhanas (for metals), which is similar to the Chinese pao zhi, although the Ayurvedic technique is more complex and may involve prayers as well as physical pharmacy techniques.[72] Rigorous evidence that the metals may be rendered nontoxic is not available, and case reports describe adverse effects to these metals.[66]

Following concerns about metal toxicity, the Government of India ruled that Ayurvedic products must specify their metallic content directly on the labels of the product.[73] The harmful effects of the samples is attributed in part to the adulterated raw material and lack of workers trained in traditional medicine.[74] In a letter to the Indian Academy of Sciences, director of the Interdisciplinary School of Health Sciences, University of Pune Patwardhan Bhushan stated that the metal adulteration is due to contamination and carelessness during the much faster modern manufacturing processes, and does not occur with traditional methods of preparation.[75] Publication of the levels of contamination found in the products has resulted in the decline of Ayurveda in India and abroad.[74]