Melatonin, a hormone that regulates sleep, which is made in the pineal gland but can also be taken as a supplement, has been observed to help reduce the severity of COVID-19 symptoms.
A June 2021 study found that COVID-19 patients given melatonin were discharged from the hospital sooner and returned to "baseline health" faster than those not given melatonin.
A September 2021 study found that melatonin improved symptoms and chances of survival in mice by reducing a type of pulmonary inflammation.
An October 2021 study reviewing melatonin's effects on humans found that "melatonin acts to prevent [oxygen deficiency], thereby improving COVID-19 prognosis."
Melatonin may also help prevent COVID-19 infection: A November 2020 study found that melatonin supplementation reduced the likelihood of a positive COVID-19 test by 28%, but authors noted that more studies are needed to evaluate its clinical efficacy.