Not Medical Advice: A round yellow pill imprinted with M on one side and imprinted with C 13 on the other side (or C/13, i.e., C over 13) is clonazepam 0.5 mg. Clonazepam is marketed primarily under the brand name Klonopin, and also Klonopin Wafer.
It is a benzodiazepine and benzodiazepine anticonvulsant used in treating anxiety, seizure disorder, panic disorder, bipolar disorder, and periodic limb movement disorder, among other conditions.
People with severe liver disease or narrow-angle glaucoma should not take clonazepam. You should consult a doctor before taking clonazepam if you have kidney or liver disease; a history of drug or alcohol addiction; a history of depression or suicidal thoughts/behavior; glaucoma; or asthma, bronchitis, chronic obstructive pulmonary disease (COPD), emphysema, or any other breathing problems.
Common side effects of clonazepam may include headache, blurred vision, runny or stuffy nose, drowsiness, difficulty thinking or with memory, slurred speech, dizziness, insomnia, fatigue, loss of appetite, skin rash, constipation, muscle weakness, drooling, weight changes, nausea, loss of coordination or balance, sore gums, or diarrhea. Those experiencing any of these common side effects on a persistent basis should consult their physician, or seek medical care immediately if experiencing any severe side effects.
According to October 2012 news reports, a recent study published in the British Medicine Journal (BMJ) showed that seniors taking benzodiazepines for insomnia or anxiety had about a 60% greater risk of developing dementia than those who do not take benzodiazepines. Medications used by the study's participants included Klonopin, Valium, Halcion, Ambien, Xanax, and Restoril.