Diltiazem, sold under the brand name Cardizem among others, is a calcium channel blocker medication used to treat high blood pressure, angina, and certain heart arrhythmias. It may also be used in hyperthyroidism if beta blockers cannot be used. It is taken by mouth or injection into a vein. When given by injection, effects typically begin within a few minutes and last a few hours.Common side effects include swelling, dizziness, headaches, and low blood pressure. Other severe side effects include an overly slow heart beat, heart failure, liver problems, and allergic reactions. Use is not recommended during pregnancy. It is unclear if use when breastfeeding is safe.Diltiazem works by relaxing the smooth muscle in the walls of arteries, resulting in them opening and allowing blood to flow more easily. Additionally, it acts on the heart to prolong the period until it can beat again. It does this by blocking the entry of calcium into the cells of the heart and blood vessels. It is a class IV antiarrhythmic.Diltiazem was approved for medical use in the United States in 1982. It is available as a generic medication. In 2019, it was the 72nd most commonly prescribed medication in the United States, with more than 10 million prescriptions. An extended release formulation is also available. Medical uses
Diltiazem is indicated for:

Stable angina (exercise-induced) – diltiazem increases coronary blood flow and decreases myocardial oxygen consumption, secondary to decreased peripheral resistance, heart rate, and contractility. Variant angina – it is effective owing to its direct effects on coronary dilation.
This results in minimal reflexive sympathetic changes.Diltiazem has negative inotropic, chronotropic, and dromotropic effects. This means diltiazem causes a decrease in heart muscle contractility – how strong the beat is, lowering of heart rate – due to slowing of the sinoatrial node, and a slowing of conduction through the atrioventricular node – increasing the time needed for each beat. Each of these effects results in reduced oxygen consumption by the heart, reducing angina, typically unstable angina, symptoms. These effects also reduce blood pressure by causing less blood to be pumped out. Research
Diltiazem is prescribed off-label by doctors in the US for prophylaxis of cluster headaches. Some research on diltiazem and other calcium channel antagonists in the treatment and prophylaxis of migraine is ongoing.Recent research has shown diltiazem may  reduce cocaine cravings in drug-addicted rats. This is believed to be due to the effects of calcium blockers on dopaminergic and glutamatergic signaling in the brain. Diltiazem also enhances the analgesic effect of morphine in animal tests, without increasing respiratory depression, and reduces the development of tolerance.Diltiazem is also being used in the treatment of anal fissures. It can be taken orally or applied topically with increased effectiveness. When applied topically, it is made into a cream form using either vaseline or Phlojel. Phlojel absorbs the diltiazem into the problem area better than the vaseline base. It has good short-term success rates. References
External links
"Diltiazem". Drug Information Portal. U.S. National Library of Medicine.