Verelan^® (verapamil hydrochloride) is a drug that is licensed to treat high blood pressure. The prescription medication works by causing the blood vessels to relax and improving blood flow. Verelan comes in the form of a capsule and is usually taken once daily in the morning. As with any drug, there are possible side effects with Verelan. A few of the more common side effects seen with this drug include constipation, headaches, and dizziness. Some of the factors that can affect the dose of Verelan that your healthcare provider prescribes include other medical conditions you may have and other medications you may currently be taking.