Diltiazem belongs to a family of medications known as calcium channel blockers. It is used alone or with other medications to treat high blood pressure and angina (chest pain). It works by relaxing blood vessels and by reducing the workload of the heart. The injectable form of this medication is sometimes used in the hospital to bring abnormal heart rhythms under control.

This medication may be available under multiple brand names and/or in several different forms. Any specific brand name of this medication may not be available in all of the forms or approved for all of the conditions discussed here. As well, some forms of this medication may not be used for all of the conditions discussed here.

Your doctor may have suggested this medication for conditions other than those listed in these drug information articles. If you have not discussed this with your doctor or are not sure why you are taking this medication, speak to your doctor. Do not stop taking this medication without consulting your doctor.

Do not give this medication to anyone else, even if they have the same symptoms as you do. It can be harmful for people to take this medication if their doctor has not prescribed it.

The recommended dose of diltiazem can range from 120 mg to 360 mg daily. The dose for the tablet form of diltiazem is usually taken 3 or 4 times a day. The dose for the capsule form of diltiazem is usually taken once daily. Swallow the capsules whole with fluids. Do not chew, crush, or open the capsules.

The starting dose of diltiazem to treat angina is usually 120 mg to 180 mg daily. Depending on how well the medication is tolerated and how effective it is at this dose, your doctor may gradually increase the dose every 1 to 2 weeks to a maximum of 360 mg daily.

The starting dose to treat high blood pressure is usually 180 mg to 240 mg daily. It may take 2 to 4 weeks to reach a maximum benefit with any one dose, therefore dose increases should not be done more often than every 2 weeks, to a maximum of 360 mg daily.

Many things can affect the dose of medication that a person needs, such as body weight, other medical conditions, and other medications. If your doctor has recommended a dose different from the ones listed here, do not change the way that you are taking the medication without consulting your doctor.

It is important to take this medication exactly as prescribed by your doctor. If you miss a dose, take it as soon as possible and continue with your regular schedule. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one. If you are not sure what to do after missing a dose, contact your doctor or pharmacist for advice.

Store this medication at room temperature, protect it from light and moisture, and keep it out of the sight and reach of children.

120 mg
Each lavender extended-release capsule marked in white ink with "Dilt HCl ER 120" contains 120 mg of diltiazem HCl. Nonmedicinal ingredients: black iron oxide, Eudragit, gelatin, hydroxypropyl methylcellulose, magnesium stearate, microcrystalline cellulose, polysorbate, povidone, simethicone, sucrose stearate, talc, and titanium dioxide. May also contain one or more of the following dyes: FD&C Red No. 28, FD&C Blue No. 1, FD&C Green No. 3, and FD&C Red No. 40.

180 mg
Each bluish-green/white extended-release capsule marked in black ink, with "Dilt HCl ER 180" contains 180 mg of diltiazem HCl. Nonmedicinal ingredients: black iron oxide, Eudragit, gelatin, hydroxypropyl methylcellulose, magnesium stearate, microcrystalline cellulose, polysorbate, povidone, simethicone, sucrose stearate, talc, and titanium dioxide. May also contain one or more of the following dyes: FD&C Red No. 28, FD&C Blue No. 1, FD&C Green No. 3, and FD&C Red No. 40.

240 mg
Each lavender/bluish-green extended-release capsule marked in white ink, with "Dilt HCl ER 240" contains 240 mg of diltiazem HCl. Nonmedicinal ingredients: black iron oxide, Eudragit, gelatin, hydroxypropyl methylcellulose, magnesium stearate, microcrystalline cellulose, polysorbate, povidone, simethicone, sucrose stearate, talc, and titanium dioxide. May also contain one or more of the following dyes: FD&C Red No. 28, FD&C Blue No. 1, FD&C Green No. 3, and FD&C Red No. 40.

300 mg
Each lavender/white extended-release capsule marked in black ink with "Dilt HCl ER 300" contains 300 mg of diltiazem HCl. Nonmedicinal ingredients: black iron oxide, Eudragit, gelatin, hydroxypropyl methylcellulose, magnesium stearate, microcrystalline cellulose, polysorbate, povidone, simethicone, sucrose stearate, talc, and titanium dioxide. May also contain one or more of the following dyes: FD&C Red No. 28, FD&C Blue No. 1, FD&C Green No. 3, and FD&C Red No. 40.

360 mg
Each bluish-green/bluish-green extended-release capsule marked in white ink with "Dilt HCl ER 360" contains 360 mg of diltiazem HCl. Nonmedicinal ingredients: black iron oxide, Eudragit, gelatin, hydroxypropyl methylcellulose, magnesium stearate, microcrystalline cellulose, polysorbate, povidone, simethicone, sucrose stearate, talc, and titanium dioxide. May also contain one or more of the following dyes: FD&C Red No. 28, FD&C Blue No. 1, FD&C Green No. 3, and FD&C Red No. 40.

Do not take diltiazem if you:

• are allergic to diltiazem or any ingredients of the medication
• are or may become pregnant
• are receiving either of the medications dantrolene or ivabradine
• have certain types of heart rhythm problems in the absence of a pacemaker
• have very low blood pressure
• have a very low heart rate (less than 40 beats per minute)
• have weakened pumping action of the heart (called left ventricular failure)
• have heart block
• have had a heart attack and are experiencing difficulty breathing

Many medications can cause side effects. A side effect is an unwanted response to a medication when it is taken in normal doses. Side effects can be mild or severe, temporary or permanent.

The side effects listed below are not experienced by everyone who takes this medication. If you are concerned about side effects, discuss the risks and benefits of this medication with your doctor.

The following side effects have been reported by at least 1% of people taking this medication. Many of these side effects can be managed, and some may go away on their own over time.

Contact your doctor if you experience these side effects and they are severe or bothersome. Your pharmacist may be able to advise you on managing side effects.

• dizziness or lightheadedness
• flushing
• general feeling of being unwell
• headache
• nausea
• red, irritated, or sore eyes
• tiredness or weakness
• vomiting

Although most of the side effects listed below don't happen very often, they could lead to serious problems if you do not seek medical attention.

Check with your doctor as soon as possible if any of the following side effects occur:

• breathing difficulty, coughing, or wheezing
• chest pain
• decreased vision
• dizziness when rising from a sitting or lying position
• fainting
• irregular or fast, pounding heartbeat
• signs of depression (e.g., poor concentration, changes in weight, changes in sleep, decreased interest in activities, thoughts of suicide)
• signs of heart problems (e.g., fast, irregular heartbeat or pulse, chest pain, sudden weight gain, difficulty breathing, leg swelling)
• signs of liver problems (e.g., nausea, vomiting, diarrhea, loss of appetite, weight loss, yellowing of the skin or whites of the eyes, dark urine, pale stools)
• skin rash
• slow heartbeat (less than 50 beats per minute)
• swelling of ankles, feet, or lower legs
• symptoms of heart block (e.g., irregular heartbeat, lightheadedness, fainting)
• symptoms of high blood sugar (e.g., frequent urination, increased thirst, excessive eating, unexplained weight loss, poor wound healing, infections, fruity breath odour)
• worsening asthma symptoms

Stop taking the medication and seek immediate medical attention if any of the following occur:

• signs of a heart attack (e.g., chest pain or pressure, pain extending through shoulder and arm, nausea and vomiting, sweating)
• signs of a serious allergic reaction (e.g., abdominal cramps, difficulty breathing, nausea and vomiting, or swelling of the face and throat)
• signs of a severe skin reaction such as blistering, peeling, a rash covering a large area of the body, a rash that spreads quickly, or a rash combined with fever or discomfort

Some people may experience side effects other than those listed. Check with your doctor if you notice any symptom that worries you while you are taking this medication.

Before you begin using a medication, be sure to inform your doctor of any medical conditions or allergies you may have, any medications you are taking, whether you are pregnant or breast-feeding, and any other significant facts about your health. These factors may affect how you should use this medication.

Asthma: Diltiazem may cause asthma symptoms to get worse. If you have asthma, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Blood pressure: Diltiazem may lower blood pressure too much in certain cases. Symptoms of severe lowering of blood pressure may occur, such as weakness or dizziness, particularly when rising suddenly from a sitting or lying position. If you experience lightheadedness, weakness, or dizziness, talk to your doctor.

Congestive heart failure: If you have congestive heart failure, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Diabetes: Diltiazem may cause an increase in blood sugar levels and glucose tolerance may change. People with diabetes may find it necessary to monitor their blood sugar more frequently while using this medication.

If you have diabetes or are at risk for developing diabetes, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Heart rhythm problems: In people with certain types of heart rhythm problems (sick sinus syndrome, second- and third-degree atrio-ventricular block) who do not have pacemakers, diltiazem may cause abnormally slow heart rates. People with certain types of heart rhythm problems should not take diltiazem. If you have a heart rhythm problem, your doctor should closely monitor your condition while you are taking diltiazem. Talk to your doctor if you have any concerns.

Kidney function: The kidneys are partially responsible for removing diltiazem from the body. As a result, kidney disease or reduced kidney function may cause this medication to build up in the body, causing side effects. If you have reduced kidney function or kidney disease, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed.

Liver function: Liver disease or reduced liver function may cause this medication to build up in the body, causing side effects. If you have liver problems, discuss with your doctor how this medication may affect your medical condition, how your medical condition may affect the dosing and effectiveness of this medication, and whether any special monitoring is needed. Your doctor may want to test your liver function regularly with blood tests while you are taking this medication.

Rarely, diltiazem may cause liver damage. If you experience symptoms of liver problems such as fatigue, feeling unwell, loss of appetite, nausea, yellowing of the skin or whites of the eyes, dark urine, pale stools, abdominal pain or swelling, and itchy skin, contact your doctor immediately.

Pregnancy: Women who are or may become pregnant should not take diltiazem. If you become pregnant while taking this medication, contact your doctor immediately.

Breast-feeding: Diltiazem passes into breast milk. If you are a breast-feeding mother and are taking diltiazem, it may affect your baby. Talk to your doctor about whether you should continue breast-feeding.

Children: The safety and effectiveness of diltiazem for use by children have not been established.

Seniors: People over the age of 65 years may be more at risk of side effects from this medication.

There may be an interaction between diltiazem and any of the following:

• acetylsalicylic acid (ASA)
• alcohol
• aldesleukin
• alpha-agonists (e.g., clonidine, methyldopa)
• alpha-blockers (e.g., alfuzosin, doxazosin, silodosin, tamsulosin)
• amiodarone
• amphetamines (e.g., dextroamphetamine, lisdexamfetamine)
• angiotensin-converting-enzyme inhibitors (ACEIs; e.g., captopril, lisinopril, ramipril)
• angiotensin receptor blockers (ARBs; e.g., candesartan, irbesartan, losartan)
• anti-cancer medications (e.g., cabazitaxel, docetaxel, doxorubicin, etoposide, ifosfamide, irinotecan, vincristine)
• antipsychotics (e.g., chlorpromazine, clozapine, haloperidol, olanzapine, quetiapine, risperidone)
• apalutamide
• apixaban
• apomorphine
• aprepitant
• "azole" antifungals (e.g., fluconazole, ketoconazole, itraconazole)
• barbiturates (e.g., butalbital, phenobarbital)
• benzodiazepines (e.g., alprazolam, clonazepam, diazepam, lorazepam, midazolam)
• beta-adrenergic blocking agents (e.g., atenolol, labetalol, metoprolol)
• bosentan
• brimonidine
• bromocriptine
• buprenorphine
• buspirone
• other calcium channel blockers (e.g., amlodipine, nifedipine, verapamil)
• calcium supplements (e.g., calcium carbonate, calcium citrate)
• cannabis
• carbamazepine
• cimetidine
• clopidogrel
• cobicistat
• colchicine
• conivaptan
• corticosteroids (e.g., budesonide, dexamethasone, fluticasone, hydrocortisone, prednisone)
• cyclosporine
• dantrolene
• darifenacin
• dexmethylphenidate
• digoxin
• dipyridamole
• disopyramide
• diuretics (water pills; e.g., furosemide, hydrochlorothiazide, triamterene)
• domperidone
• donepezil
• dronedarone
• duloxetine
• eletriptan
• enzalutamide
• eplerenone
• ergot alkaloids (e.g., dihydroergotamine, ergonovine, ergotamine, methylergonovine)
• everolimus
• flecainide
• flibanserin
• flutamide
• galantamine
• grapefruit juice
• guanfacine
• HIV non-nucleoside reverse transcriptase inhibitors (NNRTIs; e.g., efavirenz, etravirine, nevirapine, rilpivirine)
• HIV protease inhibitors (e.g., atazanavir, indinavir, ritonavir, saquinavir)
• ivabradine
• ivacaftor
• lacosamide
• lanreotide
• lemborexant
• levodopa
• lidocaine
• lithium
• lomitapide
• macrolide antibiotics (e.g., clarithromycin, erythromycin)
• maraviroc
• methadone
• methylphenidate
• mifepristone
• modafinil
• monoamine oxidase inhibitors (MAOIs; e.g., moclobemide, rasagiline, selegiline, tranylcypromine)
• nabilone
• naloxegol
• narcotic pain relievers (e.g., codeine, fentanyl, morphine, oxycodone, tramadol)
• neuro-muscular blockers (e.g., muscle relaxants; atracurium, rocuronium, succinylcholine)
• nitrates (e.g., isosorbide dinitrate, isosorbide mononitrate)
• obinutuzumab
• octreotide
• pasireotide
• pentoxifylline
• phenytoin
• phosphodiesterase-5 inhibitors (e.g., sildenafil, tadalafil, vardenafil)
• pimecrolimus
• pramipexole
• praziquantel
• primidone
• propafenone
• protein kinase inhibitors (e.g., bosutinib, dasatinib, imatinib, nilotinib)
• quinidine
• rifabutin
• rifampin
• riociguat
• rivaroxaban
• roflumilast
• ropinirole
• rotigotine
• salmeterol
• saxagliptin
• sirolimus
• solifenacin
• sphingosine 1-phosphate receptor (S1P) receptor inhibitors (e.g., fingolimod, ponesimod, siponimod)
• St. John's wort
• "statin" anti-cholesterol medications (e.g., atorvastatin, lovastatin, simvastatin)
• tacrolimus
• theophylline
• ticagrelor
• tizanidine
• tolterodine
• tolvaptan
• trazodone
• tricyclic antidepressants (e.g., amitriptyline, clomipramine, desipramine, trimipramine)
• warfarin
• zopiclone

If you are taking any of these medications, speak with your doctor or pharmacist. Depending on your specific circumstances, your doctor may want you to:

• stop taking one of the medications,
• change one of the medications to another,
• change how you are taking one or both of the medications, or
• leave everything as is.

An interaction between two medications does not always mean that you must stop taking one of them. Speak to your doctor about how any drug interactions are being managed or should be managed.

Medications other than those listed above may interact with this medication. Tell your doctor or prescriber about all prescription, over-the-counter (non-prescription), and herbal medications that you are taking. Also tell them about any supplements you take. Since caffeine, alcohol, the nicotine from cigarettes, or street drugs can affect the action of many medications, you should let your prescriber know if you use them.