The origins of yoga have been speculated to date back to pre-Vedic Indian traditions, but most likely developed around the sixth and fifth centuries BCE, in ancient India's ascetic and śramaṇa movements.[9][note 1] The chronology of earliest texts describing yoga-practices is unclear, varyingly credited to Hindu Upanishads[10] and Buddhist Pāli Canon,[11] probably of third century BCE or later. The Yoga Sutras of Patanjali date from the first half of the 1st millennium CE,[12][13] but only gained prominence in the West in the 20th century.[14] Hatha yoga texts emerged around the 11th century with origins in tantra.[15][16]
Yoga gurus from India later introduced yoga to the west,[17] following the success of Swami Vivekananda in the late 19th and early 20th century.[17] In the 1980s, yoga became popular as a system of physical exercise across the Western world.[16] Yoga in Indian traditions, however, is more than physical exercise, it has a meditative and spiritual core.[18] One of the six major orthodox schools of Hinduism is also called Yoga, which has its own epistemology and metaphysics, and is closely related to Hindu Samkhya philosophy.[19]
Many studies have tried to determine the effectiveness of yoga as a complementary intervention for cancer, schizophrenia, asthma, and heart disease. The results of these studies[20][21] have been mixed and inconclusive, with cancer studies suggesting none to unclear effectiveness, and others suggesting yoga may reduce risk factors and aid in a patient's psychological healing process.