Dal, we're so sorry to hear your tongue has become stained, and would like to help. Please know, there are many safety checks in place to ensure our products are safe to use as directed. Certain versions of Crest Pro-Health Rinse contain cetylpyridinium chloride (CPC), an ingredient that not only helps to fight plaque and gingivitis, but also kills bacteria in the mouth. For a small percentage of people who use the product, after it kills germs in your mouth, those dead germs can collect on the tooth surface and create the appearance of brown stains; especially in hard-to-brush areas. We want to assure you the discoloration is reversible and largely preventable. To help remove and prevent the discoloration, we recommend tartar-control/whitening toothpaste, a power toothbrush, and flossing. Any remaining stains can be removed with dental cleaning. We recommend you discontinue using this mouthwash, and hold onto it for two weeks, in the event our team would like to collect it. So that we can help you further, please give us a call at (800) 285-9139.