Yoga's popularity is largely due to the great benefits reaped from establishing regular practice. In addition to greater flexibility and strength, you also achieve clarity of mind and the very tangible perk of better mental health.
However, as with any physical practice, some people may experience some negative side effects, too. While the positives largely outweigh the negatives to most people, it's important to look at both sides of the yoga practice.
Positive Side Effects
Practicing even just once per week can produce a number of positive benefits for your mind and body. These include, but aren't limited to:
Improved muscular strength and flexibility: Even the Centers for Disease Control and Prevention list yoga as a viable way to fit in the recommended strength-training necessary for good health. Of course, this side effect occurs from a muscularly engaging class, such as vinyasa.
Improved cardiovascular function: Yoga may not get your heart pumping as if you were riding your bike or kickboxing, but it has notable cardiovascular side effects that include improved performance and stamina, as shown by a study published in a 2015 issue of the International Journal of Yoga.
Reduced risk of metabolic disfunction: Yoga can combat several of the factors that put you at risk for metabolic syndrome — a diagnosis that indicates inflammation and an increased chance you'll develop heart disease and type 2 diabetes. A study published in Diabetology and Metabolic Syndrome in 2015 showed that a regular yoga practice for one year lowered the blood pressure and belly fat of participants who had metabolic syndrome.
Enhanced flexibility and joint function: When you don't move your joints and muscles in a multitude of directions, you inevitably get stiff or stuck in specific patterns. Yoga is a three-dimensional way to move.
Better mental health: Yoga increases concentration, reduces mental fog and improves mental health. A review of research published in the International Journal of Yoga in 2011 reported that the practice helps with addiction, anxiety reduction and depression.
Possible Negative Side Effects
Yoga isn't all breathing and relaxation. It's a very real physical practice that can produce negative side effects.
In a small survey of 110 Finnish Ashtanga Vinyasa Yoga practitioners, published in the International Journal of Yoga Therapy in 2008, 62 percent reported a musculoskeletal injury that lasted longer than one month. But, a 2012 large survey of 2,500 Australian yoga participants published in the International Journal of Yoga, reported that almost 79 percent of yogis experienced no injury. These contrary results are likely reflective of the style of yoga practiced. Ashtanga is a vigorous practice that often requires hyperflexibility from participants, which is what most likely led to the rate of injury in that study.
Serious side effects of yoga are rare; the practice is generally considered safe. A literature review published in a 2013 issue of PLoS One reported only 76 documented cases of negative side effects occurring due to yoga:
Complications with glaucoma: Glaucoma is a condition in which extra pressure behind the eyeball eventually leads to the loss of eyesight. When you go into certain yoga positions, usually inversions including Headstand and Shoulderstand, the ocular pressure increases and could cause complications with this eye condition.
Aggravation of high blood pressure: Forceful breathing and inversion poses can also increase your blood pressure. If you have pre-existing hypertension, certain advanced yoga practices, such as Breath of Fire, could be contraindicated for you.
Back injury: Forward Folds practiced over-aggressively can irritate already vulnerable disks in your back, especially those in your lumbar spine. Overly rounding or trying to go too far before you're warmed up are ways in which you might experience a serious spinal side effect.
Muscle strain: In the PLoS One study, 27 of the adverse incidents reported affected the muscular system. This means a pull or strain to a major muscle group. An overstretch might occur when you ignore your body's warning signs and try to extend beyond your known limitations. Stretch so that you feel a mild pull, not extreme tension or pulling.
Certain populations are clearly at a greater risk of experiencing negative side effects from practicing yoga. So, if you have a pre-existing medical conditions, it's best to check with your doctor before heading to class.
Also, practicing too aggressively for your experience level and not being mindful as you move into postures will set you up for injury. To keep your side effects positive, it's wise to also practice under the guidance of a trained teacher.