The most common side effect of verapamil is constipation, affecting about 7% of people who take it. Dizziness (3.3%), nausea (2.7%), and headache (2.2%) round out the top four, based on FDA clinical trial data from nearly 5,000 patients. Most of these side effects improve as your body adjusts to the medication.
Constipation: The Most Frequent Issue
Constipation stands well above every other side effect in frequency. Verapamil works by blocking calcium channels, which relaxes blood vessels and slows the heart rate. But those same calcium channels exist throughout the muscles lining your digestive tract. When calcium can’t flow into smooth muscle cells the way it normally does, those cells contract with less force and less often. The result is slower movement of food and waste through your intestines.
Specifically, verapamil reduces the frequency and strength of the large wave-like contractions that push contents through your gut. This isn’t an indirect effect of the drug changing something else in your body. It’s a direct consequence of the same mechanism that makes verapamil useful for your heart and blood pressure.
Staying well hydrated, eating plenty of fiber-rich foods, and keeping physically active can all help counteract this slowdown. If constipation becomes persistent or uncomfortable, your prescriber can discuss whether a dose adjustment or an over-the-counter option makes sense.
Dizziness, Nausea, and Headache
About 1 in 30 people on verapamil experience dizziness, which makes sense given the drug’s ability to lower blood pressure and slow heart rate. You’re most likely to notice it when standing up quickly or after exertion. Rising slowly from a seated or lying position helps.
Nausea and headache each affect roughly 2 to 3 out of every 100 people. Some people also notice facial flushing, a warm redness in the cheeks or neck. Flushing typically fades within a few days as your body adjusts. In general, these early side effects tend to lessen over the first week or two of treatment. If they persist or interfere with your daily life, that’s worth bringing up at your next appointment rather than stopping the medication on your own.
Effects on Heart Rhythm
Because verapamil slows electrical signals through the heart, it can sometimes slow them too much. The most common sign of this is a mild delay in the electrical signal between the upper and lower chambers of the heart, something your doctor monitors through an EKG. Most people never feel this, and it doesn’t require any change in treatment.
In less than 1% of patients (about 0.8% in clinical trials), this delay progresses to a more significant block of the heart’s electrical pathway. Symptoms can include feeling unusually lightheaded, fatigued, or noticing your heart beating very slowly. This is more likely during the early phase of treatment when doses are being adjusted, because the degree of electrical slowing tracks closely with how much verapamil is in your blood. If you experience these symptoms, contact your prescriber promptly, as a dose reduction or medication change may be needed.
Who Faces Higher Risk of Side Effects
Your liver processes most of the verapamil in your body. If your liver isn’t working well, the drug clears more slowly and builds to higher levels in your blood, which amplifies every side effect. People with severe liver impairment typically need their dose reduced to about 30% of the standard amount.
Verapamil also weakens the heart’s pumping force slightly. For most people this is insignificant, but for those with heart failure, it can worsen symptoms. The American Heart Association notes that verapamil is generally not well tolerated in heart failure patients because of this effect on the heart muscle’s ability to contract.
Interactions That Increase Side Effects
Certain medications become riskier when combined with verapamil. The most well-documented example involves digoxin, a drug used for heart rhythm problems and heart failure. Verapamil can roughly double digoxin levels in the blood, raising the risk of digoxin toxicity, which causes nausea, vision changes, and dangerous heart rhythm disturbances.
Combining verapamil with beta-blockers (another class of heart rate-slowing drugs) compounds the effect on heart rate and blood pressure. Both drugs slow the heart independently, so together they can push heart rate or blood pressure dangerously low. If you’re taking either of these medications, your prescriber should already be aware and monitoring accordingly, but it’s worth confirming if you’re seeing multiple doctors who may not be coordinating prescriptions.
What to Expect in the First Few Weeks
Side effects are most noticeable during the early titration phase, when your dose is gradually being increased to find the right level. Your body is adjusting to lower blood pressure, a slower heart rate, and reduced gut motility all at once. Most people find that dizziness, nausea, headache, and flushing diminish noticeably within the first one to two weeks. Constipation, however, tends to be more persistent because it’s tied directly to how the drug works on smooth muscle, not to a temporary adjustment period. Building gut-friendly habits early (fiber, fluids, movement) is more effective than waiting to see if constipation resolves on its own.