Kombucha and rejuvelac are both fermented drinks with purported health benefits. However, both drinks have distinct differences in preparation. One is made from a culture of yeasts and bacteria, while the other is made from grains such as spelt. Proponents of each drink tout health benefits, but no clinical studies support these claims. You should consult your doctor before drinking kombucha or rejuvelac.

Proponents call kombucha a "wonder drink" and promote it as a cure-all to boost energy, metabolism and immune function, and even as a cancer cure. It is commonly known as mushroom tea, but it does not come from a mushroom. Kombucha is made by adding sugar and tea to a culture of yeast and bacteria. The culture is called a mushroom because it is gray in color and shaped like a pancake. After allowing the mixture to ferment, the resulting drink contains B vitamins. It also contains acidic compounds such as acetic acid and ethyl acetate.

Proponents say rejuvelac aids digestion and reduces inflammation. Rejuvelac is a fermented drink, but it is make differently from kombucha. Rejuvelac is typically made by fermenting spelt, rye or wheat berries in water for about three days, according to Judita Wignall in her book, "Going Raw." The resulting liquid contains beneficial bacteria known as probiotics, which aid digestion, according to Wignall. You can find a wide variety of rejuvelac recipes -- either ready-made or make-your-own -- at health food stores.

Toxins such as fungi can contaminate kombucha, which can cause illnesses, according to MayoClinic.com. Severe illness has been reported from high acid levels, including a report of one death, after drinking kombucha. Due to its capacity for toxicity, it is no longer considered safe, according to Drugs.com. Rejuvelac is not known to cause illness, with no reports of toxicity associated with drinking rejuvelac.

You should keep in mind that dietary supplements are not required to undergo safety testing and that all supplements have the capacity to cause side effects. Other than toxicity, kombucha's side effects have not been thoroughly studied, and any rejuvelac side effects have not been documented as of October 2011. If you choose to make or purchase kombucha or rejuvelac, you should only do so after discussing it with your doctor.