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Verapamil side effects and how to avoid them

Verapamil side effects include congestive heart failure, constipation, and dizziness
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By | Oct. 28, 2022 Medically reviewed by Kristi C. Torres, Pharm.D.
Rx pill bottle and prescription pad: Verapamil side effects and how to avoid them

Key takeaways

  • Verapamil is a generic prescription drug used to treat chest pain, atrial fibrillation, fast heartbeats, and high blood pressure.

  • Common side effects include constipation, dizziness, blurred vision, and nausea, but serious side effects like congestive heart failure and liver poisoning can occur, especially in those with certain pre-existing conditions.

  • Verapamil has contraindications with certain heart conditions and can interact negatively with a wide range of drugs, including heart rhythm medications, beta blockers, and substances like grapefruit.

  • To minimize side effects, patients should follow their prescription instructions carefully, avoid exceeding dosages, inform their healthcare provider about all medical conditions and medications, and attend all follow-up appointments.

In this article:

Verapamil, a generic prescription drug, is used to treat chest pain (angina), atrial fibrillation, fast heartbeats (paroxysmal supraventricular tachycardia or PSVT), and high blood pressure (hypertension). A commonly-prescribed calcium channel blocker, verapamil slows down the heart. Slower, less forceful heartbeats ease up the work demanded of the heart and, combined with verapamil’s effects on blood vessels, brings down blood pressure levels. Taken as immediate-release tablets, extended-release capsules or tablets, or given as injections, verapamil can also be taken as brand-name Verelan, Calan SR, and Isoptin SR. Possible side effects are relatively minor and uncommon, but verapamil can cause problems due to drug interactions and pre-existing conditions.

RELATED: What is verapamil? 

Common side effects of verapamil

Verapamil side effects are mild and relatively uncommon and are more likely in people taking verapamil orally than those getting injections. In clinical trials, the most common side effect of verapamil tablets was constipation, reported by 7% of participants. Most other common side effects were reported by 3% or less of participants including:

  • Infection
  • Dizziness 
  • Blurred vision
  • Nausea
  • Low blood pressure (hypotension)
  • Low energy
  • Upset stomach
  • Headache
  • Muscle cramps
  • Elevated liver enzymes
  • Fluid retention (edema)
  • Sore throat
  • Stuffy sinuses

Serious side effects of verapamil

The most serious side effects of verapamil include:

  • Congestive heart failure
  • Severely low blood pressure
  • Heart rhythm problems including slow heartbeats and heart block
  • Liver poisoning
  • Colon paralysis (paralytic ileus)
  • Severe allergic reactions

Verapamil and congestive heart failure

In people with certain pre-existing conditions, verapamil can cause congestive heart failure because of its heart-slowing effects. The estimated incidence of heart failure during verapamil treatment is 1.8%, a number high enough to cause concern. However, the majority of people who experience heart failure when taking verapamil already have heart failure or other heart conditions such as slow heartbeats or problems with the bottom chambers of the heart. It’s also more likely in people who are also taking beta blockers, another type of drug that slows down the heart. Healthcare professionals are warned to be cautious when prescribing verapamil to people with these conditions. These patients must be monitored closely, and if signs of heart failure worsen, treatment will likely need to be stopped.

How soon do verapamil side effects start?

Verapamil’s effects on the heart begin quickly, so cardiovascular adverse effects like slow heartbeats, low blood pressure, and serious heart rhythm problems could begin soon after the first dose. Most of the mild side effects happen early in treatment. Most of the serious side effects are delayed. Severe drug reactions typically take several weeks to develop, but can rapidly progress when symptoms appear.

How long do verapamil side effects last?

Side effects such as constipation, headache, dizziness, and nausea may get better over time. There also may be ways to prevent or minimize them. Side effects that don’t improve are usually reversible when the drug is stopped. This includes some serious side effects such as heart rhythm problems. How long it takes to feel better will depend on the format being prescribed, but it shouldn’t take longer than a day or two. 

What are the long-term side effects of verapamil?

Although verapamil is often used in the short-term for urgent medical conditions, it is also intended for long-term treatment, often with other drugs. There are no adverse effects specifically caused by the long-term use of verapamil.

Verapamil contraindications

Verapamil can worsen many heart conditions because it slows down the heart. In some cases, the hazards are so severe that healthcare providers are prohibited from using verapamil in people with:

  • Severe dysfunction of the lower chambers of the heart (severe ventricular dysfunction)
  • Second- to third-degree heart block (atrioventricular block) except in people with a pacemaker
  • Sick sinus syndrome (a defect in the heart’s natural pacemaker) except in people with a pacemaker
  • Atrial fibrillation or atrial flutter in cases where the heart has created its own “shortcut” to pass electrical signals from the upper chambers of the heart to the lower chambers (Wolff-Parkinson-White syndrome or Lown-Ganong-Levine syndrome)
  • Low blood pressure
  • Cardiogenic shock (the heart is not pumping enough blood)
  • Allergies to the drug

Pregnancy

Verapamil’s safety during pregnancy is unknown. Animal studies suggest that high doses can kill a fetus or slow development. Though not prohibited, verapamil is used cautiously in pregnant women.

Breastfeeding

Verapamil should not be taken when breastfeeding. The drug is present in human breast milk and is considered too risky for a nursing infant. 

Children

The FDA has not approved verapamil tablets or capsules for use in children or adolescents. However, verapamil injections are approved for use in children as young as newborns as an emergency treatment for overly rapid heartbeats (PSVT). However, though FDA-approved, it is not recommended in babies younger than 1 year old because of its effects on blood pressure.

Seniors

Because people older than 65 may have problems eliminating the drug, healthcare providers are advised to start with low doses. Verapamil is not recommended for use in older adults with heart failure.

Verapamil warnings

Although side effects are relatively uncommon, verapamil can cause serious problems in people with pre-existing conditions or if too much is taken.

Cautions

Because verapamil slows down the heart, it can cause serious problems in people with existing heart problems. Healthcare providers will be cautious and often monitor people closely if they give verapamil to anyone with the following cardiovascular conditions:

  • Slow heart rate
  • Heart failure
  • Thick heart muscles (hypertrophic cardiomyopathy)
  • Mild heart block
  • A heart valve problem called aortic stenosis
  • Mild to moderate low blood pressure

Verapamil can cause problems if people have other pre-existing medical conditions not related to the heart. These include:

  • Liver disease or kidney disease

People with liver or kidney problems do not eliminate verapamil from the body as well as others.

  • Muscular dystrophy or myasthenia gravis

Verapamil can worsen weakness caused by Duchenne’s muscular dystrophy or myasthenia gravis.

  • Constipation or obstruction

Verapamil can worsen constipation or intestinal obstruction.

  • Gastroesophageal reflux disease (GERD) or hiatal hernia

Verapamil can worsen acid reflux.

Abuse and dependence

Verapamil is not associated with physical dependence, withdrawal, or drug abuse. 

Overdose

Taking too much verapamil is considered a serious medical problem. Go to an emergency room or call a poison control center if the prescribed dose is exceeded, especially if it’s more than the maximum allowable dose of 540 mg in a single day. An overdose can cause serious cardiovascular problems including slowing the heart, lowering blood pressure, heart block, cardiac failure, or death.

Verapamil interactions

Verapamil can have serious drug interactions with a wide variety of drugs. These drug interactions fall into two major categories: drug combinations that worsen cardiovascular side effects and drug combinations that interfere with the ability of the body to break down drugs. 

The most significant interactions involve drugs that affect the heart. Some of these drugs should never be prescribed with verapamil. Others may be used, but with caution, modified dosages, or extra monitoring. These include:

Some drugs can lower blood pressure, increasing the risk for low blood pressure when taking verapamil:

Many drugs affect how well liver enzymes break down verapamil. In turn, verapamil affects how well the body breaks down an equally long list of drugs. As a result, drug levels can build up and cause side effects. For verapamil, the most worrisome ones involve throwing off heartbeats or lowering blood pressure too much. Some of the most familiar of these drugs include:

Another problem involves drugs that speed up the body’s breakdown of verapamil. That’s not good, either, because it’s like lowering the dose. These include the tuberculosis drug rifampin, stimulants, ADHD drugs, migraine drugs, NSAIDs, over-the-counter decongestants, caffeine, and the herbal supplement St. John’s wort.

How to avoid verapamil side effects

Although verapamil causes few side effects, there are ways to keep problems to a minimum. 

1. Take verapamil as instructed

Follow the prescriber’s instructions very carefully. If special instructions are given, like those for verapamil sprinkles, make sure you understand these directions before filling the prescription. 

2. Don’t take too much

Never exceed the prescribed dose of verapamil or take it more often than scheduled. The easiest way to overdose is to lose track of the dosing schedule. Use a smartphone app, paper schedule, or some other reminder to ensure doses are taken when scheduled. If a dose of verapamil is missed, it can be taken when remembered. However, if it’s almost time for the next dose, skip the missed dose and take the next dose on time. 

3. Tell the prescriber about all medical conditions

To avoid serious side effects, make sure the prescriber knows about any medical conditions past and present, especially:

  • Low blood pressure
  • Heart problems
  • Irregular heartbeats (arrhythmias)
  • Heart failure
  • Liver problems
  • Kidney problems
  • Myasthenia gravis
  • Muscular dystrophy
  • Intestinal problems or constipation
  • GERD
  • Pregnancy or pregnancy plans
  • Breastfeeding or breastfeeding plans

Make sure the prescriber is also aware of all prescription drugs, over-the-counter remedies, and dietary supplements being taken, especially beta blockers. 

4. Keep all follow-up appointments

Blood pressure may need to be checked regularly by a healthcare provider. In some cases, blood tests may be needed regularly to check liver function.

5. Avoid alcohol

Alcohol can worsen low blood pressure when combined with verapamil.

6. Avoid grapefruit

Grapefruit and grapefruit juice could increase the risk of side effects when taking verapamil.

How to treat side effects of verapamil

If side effects do happen, you’re not completely helpless. Some can be self-treated, but other issues may need professional medical attention.

Constipation

If bowel movements become a strain, drink more water and try to eat high-fiber foods. Don’t use an over-the-counter laxative until consulting with the prescribing healthcare provider. If constipation lasts for several days, report this to the prescribing healthcare provider.

Headache

If headaches are a problem, try resting and drinking fluids. Before taking an over-the-counter pain reliever, though, ask for medical advice from the prescriber. The prescriber may discourage using NSAIDs like aspirin or ibuprofen. If headaches persist or get worse, talk to the prescriber.

Headache

If dizziness comes on, sit or lie down and wait until it passes. Then stand up slowly. If dizziness gets worse or you start passing out, contact the prescriber.

Swelling of the hands and feet

To help reduce swelling, sit or lie down and elevate the feet. If swelling persists or gets worse, talk to the prescribing healthcare provider.

Low blood pressure

Unless you’re regularly checking blood pressure at home, the only way to know if blood pressure is too low is by the symptoms: lightheadedness, dizziness, and fainting. Call a healthcare professional or get medical attention.

Heart problems

Contact a healthcare professional if you experience heart palpitations, heartbeat irregularities, new or worsening chest pain, or a slow heartbeat.

Heart failure

When the heart cannot pump enough blood to the body, immediate medical attention is needed. The symptoms to watch for are swelling, rapid weight gain, and trouble breathing.

Liver problems

In rare cases, verapamil can poison the liver. A healthcare professional needs to look at this right away. Liver dysfunction must be confirmed by blood tests. Though liver dysfunction can’t be seen, it can be spotted by the symptoms:

  • Upper abdominal pain
  • Dark urine
  • Pale stools
  • Throwing up
  • Tiredness
  • Yellowing of the skin or eyes

Allergic reactions

Some people can experience a severe allergic reaction or drug reaction when taking verapamil. It’s very rare but could happen. Immediate and maybe even emergency medical care is needed, so stop taking the medicine and contact a healthcare professional if any of the following symptoms are noticed:

  • Trouble breathing
  • Shortness of breath
  • Throat tightness
  • Hives
  • Fever
  • Swelling of the throat, mouth, or face
  • Blisters
  • Sores
  • Peeling skin

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