By opening up the blood vessels to improve blood flow, Calan^® (verapamil hydrochloride) can be prescribed to treat conditions such as high blood pressure, chest pain, and certain types of irregular heart rhythms. Calan is available in brand-name and generic versions and comes in the form of a tablet. Typically, Calan is taken three or four times a day and can be taken with or without food. Although most people tolerate Calan well, there are some potential side effects of the medication, such as dizziness, nausea, and headaches. It is important to seek immediate medical attention if you believe you have overdosed on Calan.