The FDA on Friday warned against purchasing or using an oxygen concentrator at home without a valid prescription as it can lead to serious health problems such as oxygen toxicity.  The regulatory agency said that the product may be available for sale online, but that such products have not been approved by the FDA for non-prescription use.

“You should not use an oxygen concentrator at home unless it has been prescribed by a health care provider,” the FDA said in a consumer update posted on Friday. “Giving yourself oxygen without talking to a doctor first may do more harm than good. You may end up taking too much or too little oxygen. Deciding to use an oxygen concentrator without a prescription can lead to serious health problems such as oxygen toxicity caused by receiving too much oxygen. It can also lead to a delay in receiving treatment for serious conditions like COVID-19.”

Oxygen levels can be monitored with a small device called a pulse oximeter or pulse ox, which does not need to be prescribed and saw an increase in sales amid the coronavirus pandemic. However, the FDA warned that it’s possible to get a faulty or inaccurate reading if using one at home.

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Reasons for needing oxygen therapy such as an oxygen concentrator, which filters out nitrogen from the air, can include respiratory issues such as asthma, lung cancer, COPD, the flu, or COVID-19, but it should be given under the care of a physician. Breathing in high concentrations of oxygen could cause lasting lung damage while getting too little could cause damage to the heart, brain and other organs.

“If you are prescribed an oxygen concentrator for chronic health problems and have changes in your breathing or oxygen levels, or have symptoms of COVID-19, call your health care provider,” the FDA advises. “Do not make changes to the oxygen levels on your own.”