Biologically, physiologically, functionally - there's no difference between real altitude and these artificial hypoxic environments.

NPR: Anti-Doping Agency Reviews Low-Oxygen Tents

The cause of death was a hypoxic brain injury, caused by a severe decrease in oxygen to the brain.

BBC: Louise McKenzie

At higher altitudes, where atmospheric pressure is lower, oxygen enters the body less readily, leading to the hypoxic state.

WSJ: Mayo Clinic Researchers on Everest Study High Altitude's Effects on the Body

Low oxygen (hypoxic) areas known as dead zones, where most marine life cannot survive, can result in the collapse of some ecosystems.

UNESCO: NATURAL SCIENCES

He worries that if you ban the low oxygen or hypoxic tents, some may wonder why not ban those athletes who actually live at a high altitude and then train down below?

NPR: Anti-Doping Agency Reviews Low-Oxygen Tents

By studying the climbers, six of whom reached the summit, the researchers hope to gain insight into heart failure, lung disease and sleep apnea all conditions related to a low-oxygen, or hypoxic, state.

WSJ: Mayo Clinic Researchers on Everest Study High Altitude's Effects on the Body

We can't say the same for other sports, though we can remind competitors that among the array of performance enhancing aids which are available to them, such as acupuncture, hypnotism, hypoxic tents (that simulate high altitude) and the countless other perfectly legal performance enhancements are some that are probably more dangerous than drugs.

CNN: Opinion: It's time to allow doping in sport