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Drug Interaction Checker

Add your medicines – generics or brands like Cenforce, Vidalista, Eltroxin or Olmecip – and screen them for major, well-documented interactions in seconds.

Medically reviewed by John Creek [M.B.B.S] · Updated 8 Oct 2026
Check my medicines ↓
Quick answerThe most dangerous common combination is an ED tablet (sildenafil, tadalafil, vardenafil) with nitrates or poppers, which can cause a sudden drop in blood pressure. Other important ones include two QT-prolonging medicines together, spironolactone with potassium, and levothyroxine taken with calcium or iron. This tool flags these and more – always confirm with your pharmacist.
Medicines recognised100+ generics and brands
Severity levelsAvoid · Major · Moderate
SourcesFDA labels, UK SmPC, CredibleMeds
Your dataStays in your browser

Check your medicines

Add two or more medicines, then press Check. Up to 10 at a time.

Try an example:Tadalafil + isosorbideLevothyroxine + calcium + omeprazoleHCQ + azithromycinSuper Kamagra + fluoxetine
Avoid contraindicatedMajor needs prescriber actionModerate monitor or separate

This screener covers selected, well-documented interactions only. ‘No result’ does not mean a combination is safe. Always check with your pharmacist or an official checker.

How the drug interaction checker works

Type a generic name or a brand you see on a MyRxBox product page. The checker converts each brand to its active ingredients – for example, Vidalista becomes tadalafil, Eltroxin becomes levothyroxine and Super Kamagra becomes sildenafil plus dapoxetine. It then compares every pair of ingredients against a curated list of interactions documented in official prescribing information, sorts the results by severity, and links each warning to its source.

  1. Add two or more medicines, including supplements such as calcium, iron or potassium.
  2. Press Check interactions.
  3. Read each warning, open the official source, and take the results to your pharmacist or prescriber.

What the severity levels mean

LevelMeaningWhat to do
AvoidThe label says the medicines must not be used together (contraindicated).Do not combine. Speak to your prescriber about alternatives before your next dose.
MajorThe combination can cause serious harm unless the dose is changed or you are closely monitored.Contact your prescriber or pharmacist before taking them together.
ModerateThe combination can reduce how well a medicine works or cause side effects, usually manageable.Separate doses or monitor as advised, and mention it at your next review.

Important interactions by medicine

If you takeWatch out forLevel
Sildenafil, tadalafil, vardenafil (Cenforce, Vidalista, Vilitra)Nitrates, poppers, riociguatAvoid
Sildenafil, tadalafil, vardenafilRitonavir or Paxlovid, ketoconazole, itraconazole, clarithromycinMajor
Sildenafil, tadalafil, vardenafilAlpha-blockers (tamsulosin, doxazosin)Moderate
Dapoxetine (Duratia, Super Kamagra, Cenforce D)SSRIs, tramadol, strong CYP3A4 inhibitorsAvoid
Levothyroxine (Eltroxin)Calcium, iron, antacids, omeprazole, orlistat, oral semaglutideModerate
Spironolactone (Aldactone)Potassium supplements, olmesartan and other ARBs or ACE inhibitors, trimethoprimMajor
Hydroxychloroquine, azithromycin, levofloxacin, ondansetron, fluconazoleEach other and other QT-prolonging medicinesMajor
Levofloxacin, ciprofloxacin, doxycyclineCalcium, iron, zinc, antacidsModerate
Prednisolone, methylprednisolone (Medrol, Omnacortil)Naproxen, ibuprofen and other NSAIDsModerate
WarfarinFluconazole, NSAIDs, aspirin (major); ivermectin (moderate)Major
Simvastatin, lovastatinClarithromycin, ketoconazole, itraconazole, ritonavirAvoid
Pregabalin, gabapentin (Nervigesic)Opioids such as tramadol, codeine, oxycodoneMajor
Tamoxifen (Tamodex)Fluoxetine, paroxetineMajor
Naltrexone, including low dose (LDN)Opioid painkillersAvoid
Febuxostat (Febutec, Febucip)Azathioprine, mercaptopurineAvoid

Why QT prolongation matters

The QT interval is part of the heart’s electrical cycle. Some common medicines – including hydroxychloroquine, azithromycin, clarithromycin, levofloxacin, ondansetron, fluconazole, citalopram and amiodarone – can lengthen it. One medicine alone is usually low risk, but combining two or more raises the chance of a dangerous rhythm called torsades de pointes, especially in older adults, people with heart disease, and anyone with low potassium or magnesium. Your doctor may order an ECG before combining them. CredibleMeds keeps the most widely used public list of QT-risk medicines.

Timing tips that prevent interactions

  • Levothyroxine: take on an empty stomach, and keep calcium, iron and antacids at least 4 hours away.
  • Oral semaglutide (Rybelsus): take with a small sip of water at least 30 minutes before food, drink or other tablets.
  • Quinolone antibiotics and doxycycline: keep minerals and antacids several hours away from the antibiotic dose.
  • Steroids: take with food and ask whether you need stomach protection if you also use NSAIDs.

Use official checkers for a full review

No screening tool can include every medicine, supplement, herbal product, food or health condition. Kidney and liver function, age, dose and timing all change the risk. Use this tool to start the conversation, then confirm with your pharmacist or an official resource such as MedlinePlus, DailyMed or the NHS medicines A–Z. Keep an up-to-date list of everything you take and bring it to every appointment.

Medicine guides on MyRxBox

Thyroid medication guideLevothyroxine strengths, timing and interactionsLevothyroxine dosing and monitoringWhy your dose changesBlood pressure medication guideOlmesartan, metoprolol, spironolactoneOlmesartan combinationsOlmecip AM, H and Trio explainedDiabetes medication guideRybelsus, glipizide and moreOral semaglutide guideUses, safety and side effectsAsthma inhalers guideSymbicort, budesonide, montelukastBlood thinner medicationsFull list and how they differPrescription blood thinners2026 clinical guideCommon medicines and ingredientsA–Z guideGeneric equivalents directoryBrand to genericMedicine name decoderBrand vs generic, strength and formHow to read a prescription labelComplete guidePrescription vs non-prescriptionWhat is the difference?ED medication selectorSafety screen for ED tabletsAll free health toolsCalculators, trackers and more

Quick drug facts for medicines in this checker

SildenafilAvanafilLevothyroxineOlmesartanSemaglutideHydroxychloroquineAzithromycinLevofloxacinCiprofloxacinClarithromycinFluconazoleOndansetronDoxycyclineMethylprednisolonePrednisoloneNaproxenPregabalinNaltrexoneFebuxostatIvermectinFluvoxamineSimvastatinOmeprazoleFull glossary →

Drug interaction FAQs

Can I check brand names like Cenforce or Vidalista?

Yes. The checker recognises many brands sold on MyRxBox and converts them to their active ingredients before checking.

Does ‘no interaction found’ mean it is safe?

No. This tool covers selected, well-documented interactions only. Always confirm with your pharmacist or an official checker.

Can I take tadalafil with blood pressure tablets?

Many people do, but tadalafil must never be taken with nitrates, and alpha-blockers need caution. Your prescriber should review your full list.

Can I take Super Kamagra if I take an antidepressant?

Super Kamagra contains dapoxetine, which must not be used with SSRI antidepressants or within 14 days of stopping one, because of the risk of serotonin toxicity.

Why must levothyroxine be taken apart from calcium or iron?

These minerals bind levothyroxine in the gut and reduce how much is absorbed. The label advises separating them by at least 4 hours.

What is QT prolongation?

It is a change in the heart’s electrical cycle that can lead to dangerous rhythms. Several common medicines cause it, and the risk adds up when they are combined.

Can hydroxychloroquine and azithromycin be taken together?

Both can prolong the QT interval, so combining them raises the risk of heart rhythm problems. If a doctor prescribes both, they may check an ECG and your potassium and magnesium levels.

Do supplements interact with medicines?

Yes. Calcium, iron, zinc and potassium supplements are included here, but many herbal products are not. Tell your pharmacist about everything you take.

Is my medicine list saved or shared?

No. The checker runs in your browser and your list disappears when you leave the page.

What should I do if the checker shows ‘Avoid’?

Do not start the combination. If you are already taking both, do not stop a prescribed medicine suddenly – contact your prescriber or pharmacist promptly for advice.

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Sources & official guidelines

Medical disclaimer: MyRxBox tools give general information based on public labels and guidelines. They are not medical advice, a diagnosis or a prescription. Always follow your doctor or pharmacist. In an emergency, call your local emergency number.
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