500
                                This is an active ingredient in more than 100 OTC cough and cold medicines, such as Robitussin and Nyquil. In large doses it can cause euphoria, distortions of color and sound, and out-of-the-body hallucinations. Dangerous side effects include impaired judgment, vomiting, loss of muscle movement, seizures, blurred vision, drowsiness, shallow breathing, and fast heart rate.
                                What is Dextromethophan (DXM)?  It can result in withdrawal symptoms including depression and difficulty processing thoughts when the drug is stopped.