Fast XR 0 is a brand name medication containing N-Acetylcysteine (NAC) as its active ingredient. NAC is a derivative of the amino acid cysteine and is primarily used as a mucolytic agent, meaning it helps break down mucus in the airways, making it easier to clear out. It is commonly used to treat chronic respiratory conditions, such as chronic obstructive pulmonary disease (COPD), bronchitis, or cystic fibrosis, where excessive mucus production occurs. NAC also has antioxidant properties, which can help protect the body from oxidative damage and support liver function. In addition to its respiratory benefits, N-Acetylcysteine is used in emergency medicine to treat acetaminophen (paracetamol) overdoses, as it helps protect the liver from damage caused by toxic levels of the drug. Fast XR 0 refers to a specific extended-release formulation of NAC, which ensures a more consistent and prolonged release of the active ingredient in the body. Always use this medication under the guidance of a healthcare provider to avoid potential side effects.