evidence: Print OverviewDysarthria happens when the muscles used for speech are weak or are hard to control. Dysarthria often causes slurred or slow speech that can be difficult to understand. Common causes of dysarthria include conditions that affect the nervous system or that cause facial paralysis. These conditions may cause tongue or throat muscle weakness. Certain medicines also can cause dysarthria. Treating the underlying cause of dysarthria may improve your speech. You also may need speech therapy. For dysarthria caused by prescription medicines, changing or stopping the medicines may help.Products & ServicesA Book: Mayo Clinic Family Health BookNewsletter: Mayo Clinic Health Letter — Digital EditionShow more products from Mayo Clinic SymptomsSymptoms of dysarthria depend on the underlying cause and the type of dysarthria. Symptoms may include: Slurred speech. Slow speech. Not being able to speak louder than a whisper or speaking too loudly. Rapid speech that is difficult to understand. Nasal, raspy or strained voice. Uneven speech rhythm. Uneven speech volume. Monotone speech. Trouble moving your tongue or facial muscles. When to see a doctorDysarthria can be a sign of a serious condition. See a healthcare professional right away if you have sudden or unexplained changes in your ability to speak.