Kombucha tea is a fermented drink made with tea, sugar, bacteria and yeast. Although it's sometimes referred to as kombucha mushroom tea, kombucha is not a mushroom — it's a colony of bacteria and yeast. Kombucha tea is made by adding the colony to sugar and tea, and allowing the mix to ferment. The resulting liquid contains vinegar, B vitamins and a number of other chemical compounds.
Proponents claim kombucha tea helps prevent and manage serious health conditions, from blood pressure to cancer. These claims are not backed by science. Limited evidence suggests kombucha tea may offer benefits similar to probiotic supplements, including promoting a healthy immune system and preventing constipation. At present, however, valid medical studies of kombucha tea’s role in human health are very limited — and there are risks to consider.
There have been reports of adverse effects, such as stomach upset, infections and allergic reactions in kombucha tea drinkers. Kombucha tea is often brewed in homes under nonsterile conditions, making contamination likely. When improperly manufactured ceramic pots have been used for brewing, lead poisoning has occurred — the acids in the tea can leach lead from the ceramic glaze.
In short, there isn't enough evidence that kombucha tea delivers on its health claims. At the same time, several cases of harm have been reported. Therefore, the prudent approach is to avoid kombucha tea until more definitive information is available.