Isoptin SR Side Effects

Generic Name: verapamil

Note: This page contains information about the side effects of verapamil. Some of the dosage forms included on this document may not apply to the brand name Isoptin SR.

Not all side effects for Isoptin SR may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

For the Consumer

Applies to verapamil: oral capsule extended release, oral capsule extended release 24 hr, oral tablet, oral tablet extended release, oral tablet extended release 24 hr

Other dosage forms:

In addition to its needed effects, some unwanted effects may be caused by verapamil (the active ingredient contained in Isoptin SR). In the event that any of these side effects do occur, they may require medical attention.

You should check with your doctor immediately if any of these side effects occur when taking verapamil:

Less common
  • Blue lips and fingernails
  • blurred vision
  • burning, crawling, itching, numbness, prickling, "pins and needles", or tingling feelings
  • chest pain
  • confusion
  • coughing that sometimes produces a pink frothy sputum
  • difficult, fast, noisy breathing, sometimes with wheezing
  • dizziness, faintness, or lightheadedness when getting up from a lying or sitting position suddenly
  • increased sweating
  • lightheadedness, dizziness, or fainting
  • pale skin
  • shortness of breath
  • slow or irregular heartbeat
  • sore throat
  • sweating
  • swelling in legs and ankles
  • unusual tiredness or weakness
  • Chills
  • cold sweats
  • feeling of warmth
  • redness of the face, neck, arms and occasionally, upper chest

Some of the side effects that can occur with verapamil may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

More common
  • Difficulty having a bowel movement (stool)
  • headache
Less common
  • Acid or sour stomach
  • belching
  • difficulty in moving
  • heartburn
  • indigestion
  • joint pain
  • muscle aching or cramping
  • muscle pains or stiffness
  • nausea
  • rash
  • stomach discomfort, upset, or pain
  • trouble sleeping
  • unusual drowsiness, dullness, tiredness, weakness, or feeling of sluggishness
  • swollen joints

For Healthcare Professionals

Applies to verapamil: compounding powder, intravenous solution, oral capsule extended release, oral tablet, oral tablet extended release


Constipation due to verapamil (the active ingredient contained in Isoptin SR) appears to be related to a delay of colonic transit and not to an effect on upper gastrointestinal transit.

Gastrointestinal side effects have included constipation (up to 11.7%), nausea (up to 2.7%), dyspepsia (up to 2.7%), and diarrhea (up to 2.4%). Nausea (0.9%) and abdominal discomfort (0.6%) have been reported with intravenous verapamil. Nonobstructive, paralytic ileus (reversible upon discontinuation) has been reported infrequently. Diarrhea, dry mouth, gastrointestinal distress, and gingival hyperplasia have been reported during open trials/postmarketing experience.


Cardiovascular side effects have included hypotension (up to 2.5%), new or worsened congestive heart failure (CHF) or pulmonary edema (negative inotropism; 1.8%), bradycardia (heart rate less than 50/minute; 1.4%), atrioventricular (AV) block (first-degree; up to 1.7%), AV block (total first-, second-, and third-degree; 1.2%), AV block (second- and third-degree; 0.8%), and postural hypotension (up to 0.4%). Symptomatic hypotension (1.5%), bradycardia (1.2%), and severe tachycardia (1%) have been reported with intravenous verapamil (the active ingredient contained in Isoptin SR) In studies related to control of ventricular response in patients taking digoxin who had atrial fibrillation or atrial flutter, ventricular rate less than 50/minute at rest (15%) and asymptomatic hypotension (5%) were reported. Dizziness, hypotension, peripheral edema, and headache are not uncommon and are related to vasodilation of vascular smooth muscle. Verapamil may accelerate conduction of anomalous AV conduction tissue, as in the Wolff-Parkinson-White syndrome, which can result in worsened tachycardia, including malignant ventricular tachyarrhythmias or accelerated junctional tachycardia. Because of this potentially fatal side effect, verapamil is not recommended in patients with atrial fibrillation and premature ventricular depolarizations. Angina pectoris, AV block (second- and third-degree), atrioventricular dissociation, CHF, pulmonary edema, abnormal ECG, chest pain, claudication, hypertension, myocardial infarction, palpitations, and purpura (vasculitis) have been reported during open trials/postmarketing experience.

CHF or pulmonary edema may be particularly important in patients with poor left ventricular function.

Various conduction disturbances have been reported with verapamil therapy, including bradycardia, AV block, first-, second-, third-degree heart block, and left bundle branch block.

One study of patients with the Wolff-Parkinson-White syndrome (WPW) has shown that patients with a history of WPW complicated by atrial fibrillation and a history of reciprocating tachycardias with rapid conduction over an accessory pathway during atrial fibrillation are more susceptible to ventricular fibrillation after verapamil than those without a history of a rapid ventricular response. A small series of patients with WPW complicated by atrial fibrillation and a rapid ventricular response who developed cardiac arrest within 1 to 10 minutes after receiving intravenous verapamil has been reported.

The mechanism by which verapamil may enhance the ventricular rate response to atrial fibrillation is not known. Verapamil may directly shorten the refractory period of the accessory pathway or cause reflex tachycardia indirectly by causing peripheral vasodilation.

Nervous system

A 70-year-old man with supraventricular tachycardia began to experience uncontrollable, irregular, and symmetrical jerking movements in his extremities and torsional movements in his trunk 10 months after beginning verapamil (the active ingredient contained in Isoptin SR) Both myoclonic and dystonic movements occurred during activity and rest. An electroencephalogram was normal. The movements were not initiated by photic stimulation, hyperventilation, or acoustic stimuli. Once diltiazem was substituted, the movements gradually resolved over the ensuing three weeks. There was no rechallenge.

A 28-year-old woman was treated for supraventricular tachycardia with 10 mg of intravenous verapamil for 3 days in a row. After the third dose, the patient experienced involuntary movements in the buccolingual and neck muscles which made language articulation difficult. The patient also experienced episodes of compulsory neck extension and spasmodic movements of the eyes going upwards. The patient was treated with diazepam parenterally and the symptoms disappeared after 24 hours.

Nervous system side effects have included headache (up to 12.1%), dizziness (up to 4.7%), lethargy (up to 3.2%), fatigue (up to 4.5%), sleep disturbances (up to 1.4%), paresthesia (up to 1%), and rare neurologic complaints (including paresthesias, sleeping problems, and tremors; less than 1%). Dizziness (1.2%), headache (1.2%), sleepiness, vertigo, and rare cases of seizures during injection have been reported with intravenous verapamil. Rare cases of muscle fasciculations in patients with underlying neuromuscular diseases, stroke associated with verapamil-induced hypotension, exacerbation of myasthenia gravis, and myoclonic dystonia have been reported. Cerebrovascular accident, confusion, equilibrium disorders, extrapyramidal symptoms, insomnia, paresthesia, shakiness, somnolence, syncope, and tinnitus have been reported during open trials/postmarketing experience.


Other side effects have included flu syndrome (up to 3.7%), peripheral edema (up to 3.7%), edema (up to 3%), pain (up to 2.4%), fatigue (1.7%), accidental injury (up to 1.5%), ankle edema (up to 1.4%), and flushing (up to 0.8%). Asthenia has been reported during open trials/postmarketing experience.


Immunologic side effects have included infection (up to 12.1%).


A 26-year-old man with rheumatic heart disease, mitral stenosis, and supraventricular tachycardia became apneic following a 5 mg intravenous bolus of verapamil (the active ingredient contained in Isoptin SR) His heart rhythm at the time was supraventricular tachycardia at 290 beats per min; his blood pressure is not reported. The patient responded to assisted ventilation, oxygen, and DC cardioversion. The authors of this case report have located two other such cases, one of which had "stable hemodynamics," but died due to intravenous verapamil-associated acute respiratory arrest.

A 66-year-old woman with a 10-year history of hypertension and bronchial asthma was switched from immediate-release verapamil to sustained-release verapamil. The patient developed dyspnea, cough, and wheezing after taking the first tablet. The patient experienced similar reactions on three subsequent occasions with verapamil sustained-release administration.

Respiratory side effects have included upper respiratory infection (up to 5.4%), pharyngitis (up to 3%), sinusitis (up to 3%), rhinitis (up to 2.7%), and dyspnea (up to 1.4%). Extremely rare cases of respiratory arrest have been associated with the use of intravenous verapamil. The mechanism is unknown. An acute asthma attack associated with sustained-release verapamil has been reported. Dyspnea has also been reported during open trials/postmarketing experience.


Hepatic side effects have included elevated liver enzymes (up to 1.4%), and elevated transaminases with or without elevated serum bilirubin and alkaline phosphatase. The mechanism of injury is not known. Verapamil-associated hepatotoxicity is considered to be idiosyncratic, although some cases indicate a probable hypersensitivity mechanism. Elevated liver enzymes have also been reported during open trials/postmarketing experience.

Transient increases in liver function tests may occur but generally resolve following discontinuation of verapamil, although these changes may abate even with continued administration. A hypersensitivity mechanism is suspected since some cases report eosinophilic infiltrations and moderate cholestasis on liver biopsy.

Hepatic side effects may be more likely and more severe in patients with liver disease. It is recommended that verapamil therapy be reconsidered if this patient's liver disease is severe. Monitoring liver function tests during therapy is recommended.


Dermatologic side effects have included rash (up to 1.4%). Diaphoresis has been reported with intravenous verapamil (the active ingredient contained in Isoptin SR) Arthralgia and rash, exanthema, hair loss, hyperkeratosis, macules, sweating, urticaria, Stevens-Johnson syndrome, and erythema multiforme have been reported during open trials/postmarketing experience.


Endocrine side effects have rarely included interference with the release or synthesis of prolactin inhibitor factor in the hypothalamus; however, the mechanism is not known. A single case of hyperglycemic metabolic acidosis has been associated with sustained-release verapamil (the active ingredient contained in Isoptin SR) Galactorrhea/hyperprolactinemia has been reported during open trials/postmarketing experience.

Due to verapamil-induced hyperprolactinemia, rare cases of galactorrhea have been reported in both sexes.


Renal side effects have included rare cases of oliguria and worsened renal function in patients with preexisting chronic renal failure.

Rare cases of hypertensive patients with chronic renal failure who developed acute oliguric renal failure after receiving verapamil have been reported. These patients also developed symptomatic hypotension associated with slow cardiac arrhythmias.


Genitourinary side effects have included rare cases of sexual impotence and loss of libido among males. Gynecomastia, galactorrhea/hyperprolactinemia, impotence, increased urination, and spotty menstruation have been reported during open trials/postmarketing experience.

After the onset of impotence, one patient elected to discontinue verapamil. His impotence resolved upon drug discontinuation, and recurred upon rechallenge.


Musculoskeletal side effects have included myalgia (up to 1.1%) and bizarre perceptual symptoms most closely described as cold extremities. Muscle fatigue has been reported with intravenous verapamil (the active ingredient contained in Isoptin SR) Arthralgia (with rash) and muscle cramps have been reported during open trials/postmarketing experience.

Three case reports have been found by one practitioner. In each case, unusual symptoms of cold extremities and paresthesias without objective evidence of a neuromuscular or cardiac etiology were described. The symptoms resolved upon discontinuation and, in each case, recurred upon drug rechallenge.


Psychiatric side effects have included rare cases of depression. Emotional depression has been reported with intravenous verapamil (the active ingredient contained in Isoptin SR) Psychotic symptoms have been reported during open trials/postmarketing experience.


Hematologic side effects have included ecchymosis or bruising during open trials/postmarketing experience.


Hypersensitivity side effects have included aggravated allergy during open trials/postmarketing experience. In rare cases of hypersensitivity, broncho/laryngeal spasm accompanied by itch and urticaria has been reported with intravenous verapamil (the active ingredient contained in Isoptin SR)


Ocular side effects have included blurred vision during open trials/postmarketing experience. Rotary nystagmus has been reported with intravenous verapamil (the active ingredient contained in Isoptin SR)

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