Hatha yoga, or, as it is commonly called in the US, simply “yoga,” is an exercise system derived from ancient traditions in India. There are many schools or varieties of hatha yoga, but all of them involve “asanas,” or postures. Many asanas function as gentle stretching exercises, increasing flexibility. Others encourage the development of strength and balance.

The practice of hatha yoga goes beyond exercise, however. Special breathing techniques are almost always part of the process; in fact, some forms of yoga focus primarily on breathing, and therefore overlap with traditional breathing practices generally known as pranayama. Because hatha yoga originated in traditional Hindu spiritual practice, it can involve meditation, chanting, as well as philosophical and religious introspection. However, completely secular versions of hatha yoga are widely available.

Hatha yoga is believed by its practitioners to provide benefits above and beyond simple exercise. For example, certain asanas are said to address specific health problems. However, there is only minimal scientific evidence that the practice of hatha yoga actually provides any well-defined medical benefits.

How Is Hatha Yoga Used Today?

There are numerous specific schools of hatha yoga, including Iyengar yoga, Ashtanga yoga, Kriya yoga, Vini yoga, and Bikram yoga, as well as “generic” hatha yoga. Yoga is ordinarily learned through inexpensive group lessons, but regular at-home practice is necessary to progress in skill (and to derive potential health benefits). Lessons are commonly available at hospital wellness centers, health clubs, city recreation departments, and private yoga studios. There are also a wealth of do-it-yourself yoga DVDs and books, but most serious yoga practitioners caution against learning the technique without an instructor present.

What Is the Scientific Evidence for Hatha Yoga?

Although there is some evidence that yoga may offer medical benefits, in general, this evidence is not strong. There are several reasons for this (including funding obstacles), but one is fundamental: Even with the best of intentions, it is difficult to properly ascertain the effectiveness of an exercise therapy like yoga.

Only one form of study can truly prove that a treatment is effective: the double-blind, placebo-controlled trial. However, it isn’t possible to fit yoga into a study design of this type. While it might be possible to design a placebo form of yoga, it would be quite difficult to keep participants and researchers in the dark regarding who is practicing real yoga and who is practicing fake yoga!

Some compromise with the highest research standards is, therefore, inevitable. Unfortunately, the compromise used in most studies is less than optimal. In these trials, yoga has been compared to no treatment. The problem with such studies is that a treatment—any treatment—frequently appears to better than no treatment, due to a host of factors. (See Why Does This Database Rely on Double-blind Studies? for more information.) It would be better to compare yoga to generic forms of exercise, such as daily walking, but thus far this method has not seen much use.

Given these caveats, the following is a summary of what science has found out about the possible medical benefits of yoga.

Yoga, like Tai Chi, has been advocated as a means of increasing strength, balance, and physical function in seniors. However, there is as yet little scientific proof that yoga offers such benefits or that it is superior to generic exercises such as walking. There is little doubt that yoga, like any form of stretching, will increase flexibility if it is practiced consistently and over a long period of time.1

Hatha yoga is also said to relieve tension and stress. In one study of 65 women with depression and/or anxiety, a 2-month yoga program specifically designed to address these emotional conditions significantly reduced anxiety (but not depression) compared to enrolled woman who were waiting for the program to begin.24 Another study found that participation in a 6-week yoga program was associated with reduced anxiety, depression, and stress in women having radiotherapy for breast cancer.25 Adding to this evidence, 32 women who had undergone breast cancer surgery were randomized to receive just physical therapy or physical therapy plus a yoga program (called Yoga in Daily Life).32 At the end of the 3-week trial, the women in the yoga program reported less psychological distress. A trial of 122 healthy pregnant women demonstrated that daily yoga practice incorporating deep relaxation significantly reduced self-perceived stress scores compared to standard prenatal exercises.27 A large review of 35 trials involving 1,794 people found evidence to support the use of yoga to decrease stress and anxiety, although the overall quality of these studies was poor.35 Yoga was associated with reduced anxiety and in-hospital depression when compared to regular exercise in a randomized trial with 105 women in their 20th week of pregnancy. The women participated in instructor-led yoga, then continued at home through their 36th week.39 A randomized trial included 60 women who attended classes three one-hour sessions a week. Those who participated in yoga during their third trimester (weeks 26-37) of pregnancy had less pain, faster delivery, and a lower cesarean section rate when compared to standard care.45

Weak evidence hints that hatha yoga may offer modest benefits for people with chronic obstructive pulmonary disease (COPD) or asthma.2,3,11,28 For example, in one controlled study, 59 people with mild asthma were randomly assigned to practice yoga and attend a general class or simply to attend the general class.3 The results showed slight improvements in asthma in the treated group compared to the untreated group. However, even these modest benefits did not last; assessment two months later showed no difference between the groups. Furthermore, as noted above, studies in which the participants in the control group do not receive placebo treatment are inherently unreliable. A small 2009 study of 29 adults with COPD suggests that a 12-week yoga program may be associated with slight improvement in timed walking distance and self-reported functional ability in these patients.26 A special breathing technique called yogic-style Buteyko breathing may reduce medication use and subjective symptoms, though it does not appear to actually improve lung function.17,18,19

Yoga has been evalulated for its beneficial effects in a variety of chronically painful conditions, such as low back pain,12-13migraine headaches,15osteoarthritis.6 In one study, 42 people with carpal tunnel syndrome were randomly assigned to receive either yoga or a wrist splint for a period of 8 weeks.10 The results indicated that use of yoga was more effective than the wrist splint. However, participants in the control group were simply offered the wrist splint and given the choice of using it or not; it would have been preferable for them to have received a more believable placebo, like other forms of meditative exercise. In a small trial involving 53 women with fibromyalgia, those that participated in an 8-week yoga program experienced an improvement in their symptoms, including fatigue, pain, stiffness, and tenderness.31 In a review of 16 studies, researchers investigated the potential benefits of yoga in improving pain and pain-related disability in a range of conditions, including headache, back pain, irritable bowel syndrome, dialysis, muscle pain, carpal tunnel syndrome, rheumatoid arthritis, and labor pain.34 All of the studies (12 of which were randomized trials) found positive evidence to support the use of yoga.

Yoga had positive effect on chronic low back pain in a randomized trial of 80 patients. Patients randomized to treatment with a yoga program showed improvement in pain, depression, and anxiety symptoms compared to patients in physical therapy. The program was carried out in a residential setting over seven days and included technique, counseling, and educational lectures.36 Yoga had a minimal, but positive effect on chronic low back pain in a review of 12 radomized trials with 1,080 patients. Yoga was compared to no-exercise alternatives and participants were not blinded, meaning they knew which treatment they were getting. There was no clinical improvement with pain and function. It wasn't clear if yoga was better than no exercise or if adding yoga to exercise was better.44

In a randomized, controlled trial, 8 weeks of daily supervised yoga was modestly more effective than a similar amount of supervised physical exercise in relieving menopausal symptoms (eg, hot flashes), decreasing psychological stress, and improving cognitive abilities among 120 perimenopausal women.21,22

Fatigue is a common side effect of cancer treatment. In one small trial, 31 women who were still experiencing fatigue 6 months after breast cancer treatment were randomized to yoga intervention or health education.33 On average, those in the yoga group reported feeling less fatigue.

At least one study supports yoga's usefulness for congestive heart failure.23

A small trial involving 54 adolescents with eating disorders found that adding 8 weeks of yoga twice weekly to standard therapy was associated with improved eating disorder-related thoughts and behaviors.29 Yoga has also been studied for schizophrenia. In one small trial, patients who supplemented their regular treatment with a yoga program lasting 4 months had improved symptoms, were able to function better, and reported a better quality of life compared to those who did physical therapy.30 To date, only weak evidence has been reported regarding the possible usefulness of yoga for depression,4 and obsessive-compulsive disorder.20 In a review of 8 randomized trials with 457 people, schizophrenia symptoms were modestly reduced in people who participated in yoga compared to usual care. Overall, the studies had several biases (like small groups or missing results), which affect outcomes. Though yoga as a treatment may show promise, more trials will be needed to confirm benefits.42

Yoga has also been promoted as a treatment for epilepsy (seizure disorder). A review of 2 randomized trials involving 50 people found mixed results. One trial comparing real yoga to sham yoga or no treatment found that real yoga did reduce the frequency and duration of seizures. But, another trial did not support the use of yoga. The researchers emphasized the need for more studies.40,41

A review of 11 randomized trials of 800 people with moderate to high risk of cardiovascular disease found some potential benefits for yoga. Yoga for a minimum of 3 months was successful in lowering diastolic blood pressure, triglycerides, and raising high density lipoproteins (HDL, the good cholesterol) when compared to little or no intervention. However, the trials were small and of low quality, making it difficult to draw absolute conclusions about yoga's effects on blood pressure and cholesterol or how it translates to overall heart health.37 Another review analyzed the benefits of yoga when combined with conventional hypertension treatment in 120 studies with 6,693 people. In the 48 randomized trials, specific yoga techniques were associated with significant blood pressure decreases. The studies suggest a correlation between yoga and lower blood pressure, but the study populations were extremely variable, making it difficult to draw specific conclusions.38

For people with type 2 diabetes, yoga may improve fasting blood glucose, blood pressure, and both low density lipoproteins (LDL, the bad cholesterol) and HDL cholesterol. The findings are from a review of 15 randomized trials that included 1,518 patients. Yoga was compared to controls, which included standard care, walking, tai chi, lectures, and waitlisting. However, the effects did not improve HbA1c, an average measurement of blood glucose levels over a 3 month period. Yoga was done daily for 3 months.43

Some evidence suggests that hatha yoga is not helpful for chemical dependency.8

What to Expect From a Hatha Yoga Class

Yoga classes typically last about 1 to 2 hours. Most of that time is spent practicing various asanas; however, other activities such as breathing exercises may take place as well. Hatha yoga is generally a gentle, nonaerobic form of exercise. However, some types of yoga, such as Iyengar yoga, are more physically vigorous.

By the end of a yoga class, many people report feeling relaxed and comfortable, and consider this a meaningful benefit in itself. However, without regular home practice, it is unlikely that performing yoga will provide any long-term benefit. For this reason, instructors generally encourage daily practice, ranging from a few minutes to an hour or more.

Safety Issues

Hatha yoga is generally at least as safe as any other stretching-based exercise program. However there are a few hatha yoga positions, such as the headstand, that can cause injury when they are performed by a person who isn’t yet sufficiently advanced in yoga, or who has certain health problems, such as a detached retina. A properly qualified instructor can help you avoid injury, taking your own individual health status into account.