There is no certainty whether some forms of yoga are better than others, whether yoga should be prescribed to people for various health conditions, and how yoga compares with other forms of exercise. 

There's also no good evidence behind many of the supposed health benefits of yoga, like flushing out toxins and stimulating digestion.

Yoga is many things to many people. It usually involves some combination of postures and poses (asanas), regulated breathing (pranayama), and meditation and relaxation (samyama). But many classes mix in other elements, from chanting to heating to music. There's also a lot of variation in teaching quality and style. 

There can be negative consequences if done incorrectly, like any body manipulation, but if you have the right teacher this will not happen. 

Beginners should avoid advanced postures (such as headstands), and people with chronic health conditions (such as glaucoma) should consult their doctors before diving in.

Depending on the type, Yoga could build your muscles. 

It strongly depends on what you do when you do yoga. Classes that involve nothing more than lying around on piles of blankets and breathing aren't likely to strengthen your body. But more strenuous types of yoga-like ashtanga can be surprisingly similar to other forms of vigorous exercise.

Yoga might help with mood disorders, but we don't yet know for sure because the studies to date have generally been badly designed and the results are inconclusive. 

And when it comes to anxiety and depression, it can be difficult to untangle whether it's the yoga that's helping or simply the act of going out, moving your body, joining a group on a regular basis, and so on.

Researchers haven't tracked yogis over a span of 20 years or more and have not followed up to see whether they get diseases at a lower rate than non-yogis. 

There are some randomized controlled trials suggesting that yoga may improve the quality of life for diabetes patients, reduce cardiovascular disease risk factors, and even help people manage high blood pressure.