Verapamil

What it is

Verapamil is a synthetic small molecule, taken as immediate-release or extended-release tablets or given intravenously. The US label describes it as “a calcium ion influx inhibitor (slow-channel blocker or calcium ion antagonist)”. It is a non-dihydropyridine calcium channel blocker, meaning that unlike amlodipine or nifedipine it acts strongly on the heart's conducting tissue as well as on arteries. It is cleared by the liver, mainly through CYP3A4, which is why its blood levels are sensitive to other drugs and to St John's wort.

What the research says

It lowers blood pressure, relieves angina and slows a fast heart rhythm; what the outcome trials add is how that compares with alternatives. Two large randomised trials (22,576 and 16,602 participants) found a verapamil-based strategy neither better nor clearly worse than beta-blocker or diuretic-based strategies for heart attack, stroke and death; CONVINCE explicitly failed to show equivalence. A Cochrane review of 23 trials and 153,849 people found calcium channel blockers as a class probably worse than diuretics for major cardiovascular events and congestive heart failure, but better than beta-blockers for major events and stroke. Off-label, it is the usual first-choice preventive for cluster headache on a thin base of two randomised trials, and one randomised trial in children with newly diagnosed type 1 diabetes found it partly preserved insulin-producing cell function.

Evidence grade: Well established.

How it works

Drug class: Non-dihydropyridine calcium channel blocker (phenylalkylamine calcium ion influx inhibitor)

Verapamil blocks the slow channels that let calcium ions into muscle cells. In the walls of arteries that relaxes the muscle, so the arteries widen and blood pressure and the work the heart has to do both fall. In the heart's electrical wiring the same block slows conduction through the AV node, which is why it slows a fast pulse in atrial fibrillation and interrupts some supraventricular tachycardias. It does not change the total amount of calcium in the blood. (Source 1)

What it is used for

• Verapamil lowers blood pressure and, in two large randomised outcome trials, produced cardiovascular event rates very close to beta-blocker or diuretic-based regimens. CONVINCE did not demonstrate equivalence to a diuretic or beta-blocker start, and the Cochrane review of calcium channel blockers as a class found diuretics reduced major cardiovascular events and heart failure more than CCBs did. Evidence: established. (Source 2)
• This is a long-standing approved indication, and INVEST enrolled 22,576 people with coronary artery disease and hypertension, finding a verapamil-based strategy clinically as effective as an atenolol-based one. We did not find a current systematic review of verapamil versus placebo for angina symptom outcomes, so the approval rests largely on older trials summarised in the label. Evidence: limited. (Source 3)
• Approved on the strength of its effect on AV node conduction. The label's own trial data describe the trade-off directly: in digitalised patients with atrial fibrillation or flutter, resting ventricular rates below 50/min occurred in 15% and asymptomatic hypotension in 5%. We found no recent systematic review of hard outcomes for this use. Evidence: limited. (Source 3)
• Verapamil is the conventional first-choice preventive, but the controlled evidence is two randomised trials and three open-label studies with 183 patients in total. Reported benefit was about one fewer attack per day in episodic patients and benefit in about half of chronic patients. The doses used in practice are far above the labelled cardiac range, and cardiac adverse events and ECG abnormalities are described as relatively common at those doses. Evidence: limited. (Source 4)
• One double-blind randomised trial in 88 children and adolescents found verapamil partly preserved stimulated C-peptide at 52 weeks, with an adjusted between-group difference of 0.14 pmol/mL. HbA1c did not differ significantly. This is a single trial with a surrogate primary outcome and its authors call for further study. Evidence: limited. (Source 5)

Interactions

• Grapefruit juice (label): The label records that grapefruit juice may raise verapamil blood levels, which in principle could increase low blood pressure and slow the heart. A direct human pharmacokinetic study in ten hypertensive patients, however, found no effect on peak concentration or total exposure, so the strength of this interaction is disputed. (Source 6)
• Alcohol (label): Verapamil can raise blood alcohol levels and make the effects of a given amount of alcohol last longer, so the same drink goes further than expected. (Source 6)
• St John's wort (Hypericum perforatum) (pharmacokinetic study): Two weeks of St John's wort cut verapamil absorption dramatically by inducing CYP3A4 in the gut wall, so the drug can stop working at the same dose. This is a direct human jejunal perfusion study, not theory. (Source 7)
• Calcium (serum calcium above the normal range, including from supplements that raise it) (case reports): Verapamil itself does not change total serum calcium. The label records a single report suggesting that if calcium levels are above normal the drug may work less well — one report, so this is weak. (Source 8)
• Simvastatin, lovastatin and other CYP3A4-substrate statins (pharmacokinetic study): Verapamil raises statin blood levels, and the combination has been linked to muscle breakdown. Measured exposure to simvastatin was 2.5 times higher when given with verapamil. (Source 6)
• Aspirin (case reports): A few reported cases describe longer bleeding times when verapamil and aspirin are taken together than with aspirin alone. Case reports only. (Source 6)
• Digoxin and digitoxin (pharmacokinetic study): Verapamil pushes digoxin levels up substantially in the first week, which can tip someone into digitalis toxicity unless the digoxin dose is cut. (Source 9)
• CYP3A4 inhibitors and inducers (for example erythromycin, ritonavir, rifampin) (label): Verapamil is broken down by CYP3A4 and other liver enzymes, so drugs that block that enzyme push verapamil levels up and drugs that induce it push them down. (Source 6)

Stopping it

• No withdrawal syndrome or dependence is described for verapamil in the label we read. The label's discontinuation language is about managing adverse effects: progressive AV block may require a dose reduction or, rarely, stopping the drug. (Source 10)
• A Cochrane review of six randomised trials of stopping antihypertensive drugs in older people found low-certainty evidence of little or no difference in death, hospitalisation or stroke, but blood pressure rose by about 10 mmHg systolic. Note none of these trials was specific to verapamil. (Source 11)
• That same review is explicit that its evidence is too weak to settle the question, and it notes the included studies did not even measure withdrawal reactions. (Source 12)
• If verapamil is stopped in someone also taking digoxin, the digoxin dose that was reduced to allow for the interaction has to be revisited, or the person can end up under-treated. (Source 9)

What goes wrong

Against a diuretic, calcium channel blockers increased major cardiovascular events and congestive heart failure. (Source 13)

• Systematic review, Moderate certainty.
• Size: 23 RCTs with 153,849 participants.
• Who: people with hypertension starting first-line treatment.
• How long: at least two years per trial.
• Result: major cardiovascular events RR 1.05, 95% CI 1.00 to 1.09, P = 0.03; congestive heart failure RR 1.37, 95% CI 1.25 to 1.51 (moderate certainty)
• Funding: independent (Cochrane Hypertension review)

As compared to diuretics, CCBs probably increased major cardiovascular events (risk ratio (RR) 1.05, 95% confidence interval (CI) 1.00 to 1.09, P = 0.03) and increased congestive heart failure events (RR 1.37, 95% CI 1.25 to 1.51, moderate-certainty evidence).

Constipation is the most frequent adverse effect in the pooled trial data behind the label. (Source 14)

• Randomized trial, Certainty not rated.
• Size: 4,954 patients in clinical trials of orally administered verapamil.
• Who: people treated with oral verapamil in clinical trials.
• How long: not stated in this label section.
• Result: constipation 7.3%, dizziness 3.3%, nausea 2.7%, hypotension 2.5%, headache 2.2%, edema 1.9%, congestive heart failure or pulmonary edema 1.8%, fatigue 1.7%, dyspnea 1.4%, bradycardia (HR <50/min) 1.4%, AV block 1.2%, rash 1.2%.
• Funding: not stated (manufacturer-submitted registration data)

The following reactions to orally administered verapamil occurred at rates greater than 1% or occurred at lower rates but appeared clearly drug-related in clinical trials in 4,954 patients:

In digitalised patients with atrial fibrillation or flutter, excessive slowing of the heart was common. (Source 14)

• Randomized trial, Certainty not rated.
• Size: not stated in this label section.
• Who: digitalised patients with atrial fibrillation or flutter in clinical trials.
• How long: not stated in this label section.
• Result: resting ventricular rates below 50/min in 15% of patients; asymptomatic hypotension in 5%.
• Funding: not stated (manufacturer-submitted registration data)

ventricular rates below 50 at rest occurred in 15% of patients and asymptomatic hypotension occurred in 5% of patients

Verapamil can block AV conduction; higher-degree AV block occurred in a small percentage. (Source 10)

• Randomized trial, Certainty not rated.
• Size: not stated in this label section.
• Who: people taking verapamil, especially during early dose titration.
• How long: especially the early titration phase.
• Result: higher degrees of AV block in 0.8%.
• Funding: not stated (manufacturer-submitted registration data)

Higher degrees of AV block, however, were infrequently (0.8%) observed.

Bleeding other than stroke was more common on verapamil than on atenolol or hydrochlorothiazide. (Source 15)

• Randomized trial, Certainty not rated.
• Size: 16,602 participants.
• Who: people with hypertension plus another cardiovascular risk factor.
• How long: mean 3 years.
• Result: non-stroke haemorrhage 118 with COER verapamil versus 79 with atenolol or hydrochlorothiazide; HR 1.54, 95% CI 1.16 to 2.04, P = .003.
• Funding: industry-sponsored.

Nonstroke hemorrhage was more common with participants in the COER-verapamil group (n = 118) compared with the atenolol or hydrochlorothiazide group (n = 79) (HR, 1.54 [95% CI, 1.16-2.04]; P =.003).

An international Delphi consensus study of 22 cardiac-rhythm experts states in its background that cardiac adverse events and ECG abnormalities are relatively common at the high verapamil doses used for cluster headache, and that evidence-based screening and monitoring guidelines are lacking. (Source 16)

• Official position, Very low certainty.
• Size: 22 international clinical experts in cardiac rhythm disorders, by Delphi method.
• Who: cluster headache patients on high-dose verapamil.
• How long: not applicable.
• Result: no rate given; the panel agreed only on a pretreatment ECG, half advised Holter ECG at verapamil ≥ 480 mg/day, and highest recommended daily doses varied between 240 and 960 mg.
• Funding: not stated in the abstract.

Limit of this finding: This is expert consensus, not trial evidence. Twenty-two specialists were polled by the Delphi method; the panel agreed only on doing an ECG before treatment, and half of them advised Holter monitoring above 480 mg a day. The highest daily dose the panellists would recommend ranged from 240 mg to 960 mg, which is itself a measure of how little agreement there is. None of this rests on a trial measuring how often harm occurs.

Although cardiac adverse events and EKG abnormalities are relatively common, evidence-based guidelines for screening and monitoring patients on HDV are lacking.

What the evidence supports

A verapamil-based strategy produced the same rate of death, heart attack and stroke as an atenolol-based strategy in people with both hypertension and coronary artery disease. (Source 2)

• Randomized trial, Certainty not rated.
• Size: 22,576 participants; 61,835 patient-years of follow-up.
• Who: hypertensive patients aged 50 or older with coronary artery disease, at 862 sites in 14 countries.
• How long: mean 2.7 years per patient.
• Result: primary outcome 9.93% with the calcium antagonist strategy versus 10.17% without; relative risk 0.98, 95% CI 0.90 to 1.06; absolute difference 0.24 percentage points.
• Funding: not stated in the abstract (INVEST was supported by industry and by the University of Florida)

2269 patients had a primary outcome event with no statistically significant difference between treatment strategies (9.93% in CAS and 10.17% in NCAS; relative risk [RR], 0.98; 95% confidence interval [CI], 0.90-1.06).

Compared with beta-blockers, calcium channel blockers as a first-line class reduced major cardiovascular events and stroke. (Source 13)

• Systematic review, Moderate certainty.
• Size: 23 RCTs with 153,849 participants (18 dihydropyridine, 4 non-dihydropyridine, 1 unspecified)
• Who: people with hypertension, followed at least two years.
• How long: at least two years per trial.
• Result: major cardiovascular events RR 0.84, 95% CI 0.77 to 0.92; stroke RR 0.77, 95% CI 0.67 to 0.88 (moderate certainty); cardiovascular mortality RR 0.90, 95% CI 0.81 to 0.99 (low certainty)
• Funding: independent (Cochrane Hypertension review)

As compared to beta-blockers, CCBs reduced the following outcomes: major cardiovascular events (RR 0.84, 95% CI 0.77 to 0.92), stroke (RR 0.77, 95% CI 0.67 to 0.88, moderate-certainty evidence), and cardiovascular mortality (RR 0.90, 95% CI 0.81 to 0.99, low-certainty evidence).

In children and adolescents with newly diagnosed type 1 diabetes, verapamil partly preserved stimulated insulin-producing cell function at one year. (Source 5)

• Randomized trial, Certainty not rated.
• Size: 88 participants randomised (47 verapamil, 41 placebo); 83 completed.
• Who: children and adolescents aged 7 to 17 with newly diagnosed type 1 diabetes weighing 30 kg or more, 6 US centres.
• How long: 52 weeks from diagnosis.
• Result: C-peptide area under the curve 0.65 pmol/mL versus 0.44 pmol/mL at 52 weeks; adjusted between-group difference 0.14 pmol/mL, 95% CI 0.01 to 0.27, P = .04; HbA1c 6.6% versus 6.9%, difference -0.3%, 95% CI -1.0% to 0.4% (not significant)
• Funding: not stated in the abstract.

In the verapamil group, the mean C-peptide area under the curve was 0.66 pmol/mL at baseline and 0.65 pmol/mL at 52 weeks compared with 0.60 pmol/mL at baseline and 0.44 pmol/mL at 52 weeks in the placebo group (adjusted between-group difference, 0.14 pmol/mL [95% CI, 0.01 to 0.27 pmol/mL]; P = .04).

Verapamil's standing as the first-choice preventive for cluster headache rests on two controlled trials and three open-label studies in 183 patients in total. (Source 4)

• Expert review, not systematic, Very low certainty.
• Size: 183 cluster headache patients across 2 randomised controlled studies and 3 open-label studies.
• Who: people with episodic and chronic cluster headache.
• How long: not stated in the abstract.
• Result: verapamil 360 mg/day in both controlled studies; about half of chronic patients benefited; episodic patients' attack burden reduced by on average 1 attack/day.
• Funding: not stated in the abstract.

Clinical preventive treatment of CH with verapamil is based on 2 randomized controlled studies and 3 open-label studies. In total, 183 CH patients participated.

What the evidence does not support

A verapamil-based regimen failed to demonstrate equivalence to a diuretic or beta-blocker regimen for preventing cardiovascular disease. (Source 17)

• Randomized trial, Certainty not rated.
• Size: 16,602 participants at 661 centres in 15 countries.
• Who: people with hypertension plus at least one other cardiovascular risk factor.
• How long: mean 3 years; the sponsor closed the study early, before unblinding.
• Result: 364 primary events with COER verapamil versus 365 with atenolol or hydrochlorothiazide; hazard ratio 1.02, 95% CI 0.88 to 1.18, P = .77; all-cause mortality HR 1.08, 95% CI 0.93 to 1.26.
• Funding: industry-sponsored; the sponsor closed the study before unblinding.

The CONVINCE trial did not demonstrate equivalence of a COER verapamil-based antihypertensive regimen compared with a regimen beginning with a diuretic or beta-blocker.

Grapefruit juice, which the label warns may raise verapamil levels, had no measurable effect on verapamil pharmacokinetics in a direct human study. (Source 18)

• Blood level study, Very low certainty.
• Size: 10 hypertensive patients.
• Who: adults on chronic verapamil treatment.
• How long: two days, one with water and one with grapefruit juice.
• Result: no effect on Cmax, tmax or AUC; the ratio of parent drug to metabolite rose slightly, 1.67 to 1.92.
• Funding: not stated in the abstract.

Limit of this finding: This small study contradicts itself slightly. Its results section says the ratio of verapamil to its metabolite was "slightly, but significantly, increased" after grapefruit juice, while its conclusion says grapefruit juice has "no significant effect". Both are the authors' own words. What the study does show is that the amount of verapamil in the blood (Cmax and AUC) did not change in 10 patients after a single glass; it does not show that grapefruit juice has been ruled out as an interaction, and the manufacturer's label still warns about it.

A single administration of GJ with short-acting verapamil has no significant effect on the pharmacokinetics, of verapamil.

Only 4 of the 23 trials in the Cochrane review used a non-dihydropyridine such as verapamil, so the class results are mostly about other calcium channel blockers. (Source 13)

• Systematic review, Moderate certainty.
• Size: 23 RCTs with 153,849 participants, of which 4 used non-dihydropyridines.
• Who: people with hypertension.
• How long: at least two years per trial.
• Result: 18 dihydropyridine trials, 4 non-dihydropyridine, 1 not specified.
• Funding: independent (Cochrane Hypertension review)

We included a total of 23 RCTs (18 dihydropyridines, 4 non-dihydropyridines, 1 not specified) with 153,849 participants with hypertension.

All-cause mortality did not differ between calcium channel blockers and any other antihypertensive class. (Source 13)

• Systematic review, Moderate certainty.
• Size: 23 RCTs with 153,849 participants.
• Who: people with hypertension.
• How long: at least two years per trial.
• Result: no difference in all-cause mortality reported between first-line CCBs and any other class.
• Funding: independent (Cochrane Hypertension review)

All-cause mortality was not different between first-line CCBs and any other antihypertensive classes.

Where the research disagrees

Whether grapefruit juice meaningfully raises verapamil levels

• US prescribing information for verapamil hydrochloride tablets (DailyMed SPL, 2024), position: Grapefruit juice: Grapefruit juice may increase plasma levels of verapamil. (Source 6)
• Ho and colleagues, European Journal of Clinical Pharmacology 1998, crossover pharmacokinetic study in 10 hypertensive patients, pharmacokinetic: GJ did not affect Cmax, tmax, AUCv or AUVm. (Source 19)

Whether calcium channel blockers should be a first-line choice for hypertension

• Cochrane Hypertension review of 23 RCTs and 153,849 participants, 2022, systematic-review: For the treatment of hypertension, there is moderate certainty evidence that diuretics reduce major cardiovascular events and congestive heart failure more than CCBs. (Source 20)
• INVEST investigators, JAMA 2003, randomised trial in 22,576 hypertensive patients with coronary artery disease, rct: The verapamil-trandolapril-based strategy was as clinically effective as the atenolol-hydrochlorothiazide-based strategy in hypertensive CAD patients. (Source 21)

How much

• Reference intake: Dosing is set by the prescriber, not by the reader. As a regulatory position, the US immediate-release tablet label (DailyMed SPL published 23 December 2024) states the dose must be individualised by titration, and that the usual initial monotherapy dose for hypertension in clinical trials was 80 mg three times a day. (Source 22)
• Upper limit: The same label states that the usefulness and safety of dosages exceeding 480 mg/day have not been established and that this daily dose should not be exceeded. For hypertension it adds that there is no evidence that doses beyond 360 mg/day provide added effect. Expert opinion for cluster headache goes far beyond this, with highest recommended daily doses in a Delphi panel varying between 240 and 960 mg. (Source 22)
• Studied: For angina, clinical trials used 80 mg to 120 mg three times a day. (Source 23)
• Studied: For rate control in digitalised chronic atrial fibrillation, 240 to 320 mg/day in divided doses; for prophylaxis of paroxysmal supraventricular tachycardia in non-digitalised patients, 240 to 480 mg/day in divided doses. (Source 23)
• Studied: CONVINCE randomised 8,241 participants to 180 mg of controlled-onset extended-release verapamil as the starting dose. (Source 15)
• Studied: Both randomised cluster headache studies used verapamil 360 mg/day. (Source 4)
• Studied: For essential hypertension, the label records that the usual initial monotherapy dose in clinical trials was 80 mg three times a day (240 mg/day). (Source 24)

A common belief, and what the research shows

The belief: Verapamil is just another blood pressure pill, interchangeable with amlodipine or a water tablet.

What the research shows: It belongs to a different branch of the calcium channel blockers. Unlike the dihydropyridines, it acts directly on the heart's conducting tissue: the label states that “By decreasing the influx of calcium, verapamil prolongs the effective refractory period within the AV node and slows AV conduction in a rate-related manner.” That is why it is used for atrial fibrillation and SVT, and also why higher-degree AV block occurred in 0.8% of trial patients and resting rates below 50/min in 15% of digitalised patients with atrial fibrillation. The Cochrane review that is often cited for calcium channel blockers in hypertension is also mostly not about verapamil: only 4 of its 23 trials used a non-dihydropyridine.

Questions and answers

What is it?

Verapamil is a manufactured medicine, not a nutrient. It is a calcium channel blocker of the phenylalkylamine type, taken as immediate-release or extended-release tablets or given by injection in hospital. The US label describes it as a calcium ion influx inhibitor that works by changing how calcium crosses the membranes of artery muscle cells and heart cells. (Source 1)

What does it do in the body?

Two things at once. In artery walls it relaxes muscle, so the arteries widen, resistance falls and blood pressure drops, which also reduces the work the heart has to do and so relieves effort angina. In the heart's electrical wiring it slows conduction through the AV node, which is why it brings down a fast pulse in atrial fibrillation and can stop some supraventricular tachycardias. It does not change the total calcium in your blood. (Source 25)

Is it good or bad for you?

It depends on what it is being used for and what the alternative is. In 22,576 people with coronary artery disease and hypertension, a verapamil-based strategy matched an atenolol-based one for death, heart attack and stroke. As a class, though, calcium channel blockers came out worse than diuretics for major cardiovascular events and heart failure in the Cochrane review, and better than beta-blockers. The commonest everyday problem is constipation, at 7.3% in pooled trials, and the serious ones are excessive slowing of the heart and AV block. (Source 20)

How do you get more of it?

Verapamil is a prescription-only drug and there is no food, supplement or behaviour that supplies it; the dose is set and adjusted by a prescriber. What trials used is on record: for angina, 80 mg to 120 mg three times a day; for rate control in digitalised atrial fibrillation, 240 to 320 mg/day in divided doses. The label says the dose must be individualised by titration. (Source 22)

If it is harmful, what reduces it?

If verapamil levels are too high the ways down are stopping or reducing the drug, and avoiding the things that raise its level — CYP3A4 inhibitors such as erythromycin or ritonavir. In the opposite direction, a CYP3A4 inducer strips it out of the body: two weeks of St John's wort cut verapamil exposure by about 78 to 80%, which is a loss of treatment rather than a remedy. In an overdose or severe reaction the label describes emergency measures given in hospital, including intravenous calcium gluconate. (Source 6)

Why might someone be low in it or missing it?

Nobody is naturally short of verapamil; it is a drug, not something the body makes. Blood levels can end up lower than intended for identifiable reasons: a CYP3A4 inducer such as rifampin or St John's wort speeds its breakdown, and the St John's wort study showed exposure falling by roughly 80% through induction of first-pass metabolism in the gut. Missed doses and the drug simply not having been prescribed are the other obvious reasons. (Source 26)

Which whole foods contain it or feed it?

No whole food contains verapamil. The food questions that matter run the other way: grapefruit juice is listed in the label as possibly raising verapamil levels, although a direct study in ten patients found no measurable effect; alcohol interacts because verapamil can raise blood alcohol levels and prolong their effects; and the extended-release form is directed to be taken with food. There is no dietary way to obtain or boost the drug. (Source 6)

What happens if you do not have it?

Not taking verapamil is not a deficiency; the question is what happens to the condition it was treating. For high blood pressure, a Cochrane review of six randomised trials of stopping antihypertensives in older people found blood pressure about 10 mmHg higher systolic in those who stopped, with low-certainty evidence of little or no difference in death, hospitalisation or stroke over follow-up of 4 to 56 weeks. For rate control or angina, stopping removes the effect on the AV node and on arterial tone that the drug was prescribed for. (Source 12)

How can you test for it?

Routine blood level testing of verapamil is not part of ordinary care. What is monitored is its effects: blood pressure, pulse and the ECG, because PR-interval prolongation tracks verapamil plasma concentrations, especially during early dose titration. For high-dose use in cluster headache, an international expert panel agreed on a pretreatment ECG to screen for pre-existing arrhythmia but reached no consensus on monitoring during treatment, which tells you how weak the evidence base for monitoring is. (Source 10)

References

1. DailyMed (US National Library of Medicine), FDA Structured Product Label. Verapamil Hydrochloride Tablets, USP - CLINICAL PHARMACOLOGY, opening paragraph (Full Prescribing Information). 2024. Read the source
2. JAMA. A calcium antagonist vs a non-calcium antagonist hypertension treatment strategy for patients with coronary artery disease. The International Verapamil-Trandolapril Study (INVEST): a randomized controlled trial. (Results). 2003. PMID 14657064, DOI 10.1001/jama.290.21.2805. Read the source
3. DailyMed (US National Library of Medicine), FDA Structured Product Label. Verapamil Hydrochloride Tablets, USP - INDICATIONS AND USAGE (Full Prescribing Information). 2024. Read the source
4. Headache. Verapamil and Cluster Headache: Still a Mystery. A Narrative Review of Efficacy, Mechanisms and Perspectives. (Results). 2019. PMID 31339562, DOI 10.1111/head.13603. Read the source
5. JAMA. Effect of Verapamil on Pancreatic Beta Cell Function in Newly Diagnosed Pediatric Type 1 Diabetes: A Randomized Clinical Trial. (Results). 2023. PMID 36826844, DOI 10.1001/jama.2023.2064. Read the source
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11. Cochrane Database of Systematic Reviews. Withdrawal of antihypertensive drugs in older people. (Main results: blood pressure, falls and sources of bias). 2025. PMID 40162571, DOI 10.1002/14651858.CD012572.pub3. Read the source
12. Cochrane Database of Systematic Reviews. Withdrawal of antihypertensive drugs in older people. (Authors' conclusions). 2025. PMID 40162571, DOI 10.1002/14651858.CD012572.pub3. Read the source
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18. European Journal of Clinical Pharmacology. The effect of grapefruit juice on the pharmacokinetics of orally administered verapamil. (Conclusions). 1998. PMID 9696960, DOI 10.1007/s002280050470. Read the source
19. European Journal of Clinical Pharmacology. The effect of grapefruit juice on the pharmacokinetics of orally administered verapamil. (Results). 1998. PMID 9696960, DOI 10.1007/s002280050470. Read the source
20. Cochrane Database of Systematic Reviews. Calcium channel blockers versus other classes of drugs for hypertension. (Authors' conclusions). 2022. PMID 35000192, DOI 10.1002/14651858.CD003654.pub6. Read the source
21. JAMA. A calcium antagonist vs a non-calcium antagonist hypertension treatment strategy for patients with coronary artery disease. The International Verapamil-Trandolapril Study (INVEST): a randomized controlled trial. (Conclusion). 2003. PMID 14657064, DOI 10.1001/jama.290.21.2805. Read the source
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23. DailyMed (US National Library of Medicine), FDA Structured Product Label. Verapamil Hydrochloride Tablets, USP - DOSAGE AND ADMINISTRATION, Angina and Arrhythmias (Full Prescribing Information). 2024. Read the source
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26. Clinical Pharmacology and Therapeutics. St John's wort decreases the bioavailability of R- and S-verapamil through induction of the first-pass metabolism. (Conclusions). 2004. PMID 15060508, DOI 10.1016/j.clpt.2003.12.012. Read the source