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Verapamil

Medication calcium channel blocker heart & blood pressure
Aka: Isoptin
Brands seen in Singapore: Isoptin SR
Not medical advice. Check with your doctor or pharmacist before you start, stop or change the timing of anything you take.
How to use
What it’s for
HealthHub: irregular heartbeats and high blood pressure
When to take
HealthHub: with or without food; sr tablets swallowed whole
Take with
Water · HealthHub: grapefruit raises the side-effect risk
Pros & cons
Pros
  • NHS: it starts working on the day it is started
  • HealthHub: relaxes and widens blood vessels
  • SG label: usually one 240 mg sr tablet in the morning
Cons
  • NHS: constipation is the most common side effect
  • HealthHub: it can slow the heart rate further
  • HealthHub: very rarely it can injure the liver
Sources
  1. HSA — Listing of Registered Therapeutic Products (data.gov.sg open dataset, 5,511 rows, cached in full and filtered locally) · read 2026-08-27
    what it says
    “Exactly one registered verapamil product: 'ISOPTIN SR TABLET 240 mg' [SIN00344P], Verapamil Hydrochloride, Forensic classification 'Prescription Only', ATC C08DA01, licence holder Abbott Laboratories (Singapore)”
  2. National Drug Formulary (SG, MOH) — ISOPTIN SR TABLET 240 MG [SIN00344P], approved indication and posology · read 2026-08-27
    what it says
    “the daily dose for adults is 1 film coated tablet in the morning … the dose can be raised to a maximum of 2 film coated tablets daily … a daily dose of 480mg should not be exceeded”
  3. HealthHub (National Medication Information workgroup, SG) — Verapamil: what is this medication for · read 2026-08-27
    what it says
    “Verapamil is used to treat certain heart conditions such as irregular heartbeats. It can also be used to lower your blood pressure by relaxing and widening blood vessels.”
  4. HealthHub — Verapamil: how should I take or use this medication · read 2026-08-27
    what it says
    “You may take this medication with or without food. If you are taking a sustained release tablet, you should swallow the tablet whole. Do not chew or crush sustained release forms of verapamil”
  5. HealthHub — Verapamil: what precautions should I take · read 2026-08-27
    what it says
    “This medicine can cause the heart rate to be slower and should be used with caution with other medicines that slow the heart rate e.g. digoxin, beta blockers and amiodarone.”
  6. HealthHub — Verapamil: common and rare but serious side effects · read 2026-08-27
    what it says
    “Leg swelling, headache and constipation … are some common side effects … This medicine may decrease your heart rate … Very rarely, this medicine can injure or damage the liver.”
  7. HealthHub — Verapamil: what food or medication should I avoid · read 2026-08-27
    what it says
    “Avoid taking grapefruit when you are taking this medicine as grapefruit may interact with your medicine and increase the risk of side effects.”
  8. NHS — About verapamil, Key facts · read 2026-08-27
    what it says
    “Verapamil starts to work on the day you start taking it, but it may take 1 to 2 weeks to work fully. The most common side effect of verapamil is constipation. Do not eat grapefruit”
  9. NHS — Side effects of verapamil · read 2026-08-27
    what it says
    “Common side effects of verapamil … Constipation … Feeling or being sick … Flushing … Headaches”
  10. NHS — Who can and cannot take verapamil · read 2026-08-27
    what it says
    “tell your doctor or pharmacist if you: … have low blood pressure … have any other heart problems, including heart failure, or a very slow or irregular heart rate have Wolff-Parkinson-White syndrome … myasthenia gravis”
  11. NHS — Taking verapamil with other medicines and herbal supplements · read 2026-08-27
    what it says
    “antibiotics, such as clarithromycin, erythromycin or rifampicin antifungal medicines, such as itraconazole digoxin or ivabradine … statins … such as simvastatin or atorvastatin … St John's wort … can affect the way verapamil works”
  12. NHS — Dosage and strength of verapamil · read 2026-08-27
    what it says
    “If you're taking slow-release tablets, the usual dose is 240mg, taken once a day. Your doctor may increase it to 480mg a day.”
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Updated 2026-08-29. Every line above traces to a numbered source. Kozen-X is not a medical device and does not give medical advice. It lists what published sources have written down — nothing more. A pair not listed is unrecorded, not cleared. Before you start, stop or re-time anything, talk to your doctor or pharmacist.