If you're taking terbinafine for a stubborn fungal infection-like athlete’s foot, nail fungus, or ringworm-you already know how frustrating it can be. But what you might not know is that this common antifungal can cause serious problems if mixed with certain other drugs. Terbinafine isn’t just another pill you pop. It affects how your liver processes other medications, and that can turn a routine prescription into a medical emergency.
Why terbinafine interacts with other drugs
Terbinafine is broken down in your liver by enzymes called CYP2D6 and, to a lesser extent, CYP3A4. These are the same enzymes that handle over 25% of all prescription drugs. When terbinafine blocks or slows them down, other drugs build up in your bloodstream. That’s when side effects get dangerous.
For example, if you're taking a beta-blocker like metoprolol for high blood pressure, terbinafine can make it stick around longer than it should. That can drop your heart rate too low. Or if you’re on a medication for depression like fluoxetine, terbinafine can push its levels into toxic range-leading to serotonin syndrome, a rare but life-threatening condition.
Medications you must avoid with terbinafine
Here are the top drugs that should never be taken with terbinafine, based on FDA warnings and clinical studies:
- Tricyclic antidepressants (amitriptyline, nortriptyline, imipramine): These can cause heart rhythm problems when terbinafine raises their levels. Risk of QT prolongation and sudden cardiac arrest goes up.
- SSRIs and SNRIs (fluoxetine, paroxetine, venlafaxine): Combined with terbinafine, they can trigger serotonin syndrome-symptoms include high fever, confusion, rapid heartbeat, and muscle stiffness.
- Beta-blockers (metoprolol, propranolol, atenolol): Terbinafine can increase their concentration by up to 50%, leading to dangerously low blood pressure or bradycardia.
- Codeine and tramadol: These rely on CYP2D6 to become active. Terbinafine blocks that process, making them useless for pain relief. Worse, if you’re taking tramadol, you lose its pain control and still get its seizure risk.
- Antiarrhythmics (quinidine, flecainide, propafenone): Terbinafine can cause these drugs to accumulate, leading to irregular heartbeats or even cardiac arrest.
- Propranolol and metoprolol: Both are high-risk when paired with terbinafine. Studies show a 40-60% increase in blood levels, which can cause dizziness, fainting, or heart failure in older adults.
Even over-the-counter meds can be risky. Cold medicines containing dextromethorphan (like Robitussin DM) can interact badly. So can some herbal supplements-St. John’s wort, for example, alters liver enzymes and can make terbinafine less effective or more toxic.
What about common painkillers?
Acetaminophen (Tylenol) is generally safe with terbinafine. But here’s the catch: both are processed by the liver. If you're taking high doses of acetaminophen daily-say, for chronic back pain-you’re already stressing your liver. Add terbinafine, and you’re doubling down on risk.
NSAIDs like ibuprofen or naproxen are usually okay in low doses, but not if you have kidney problems or are over 65. Terbinafine can slightly reduce kidney clearance of these drugs, raising the chance of stomach bleeding or fluid retention.
Bottom line: Don’t assume OTC means safe. Always check with your pharmacist before adding anything new.
What about alcohol?
There’s no direct interaction between terbinafine and alcohol. But here’s the real issue: both are metabolized by the liver. Drinking while on terbinafine increases your risk of liver damage. The FDA has issued warnings about terbinafine causing severe liver injury in rare cases-and alcohol makes that risk worse.
If you drink regularly, your doctor should test your liver enzymes before you start terbinafine. And if you’re on it? Cut back. One glass of wine a week might be fine. Daily beer or cocktails? Not worth the risk.
What about birth control or hormones?
Terbinafine doesn’t directly interfere with estrogen or progesterone. So your birth control pill, patch, or IUD should still work. But some people report breakthrough bleeding or nausea while taking terbinafine. That’s not because the hormones failed-it’s because your liver is overloaded.
If you’re on hormone replacement therapy (HRT) or taking tamoxifen for breast cancer, talk to your oncologist. Tamoxifen is metabolized by CYP2D6, and terbinafine can reduce its effectiveness. That’s a serious concern if you’re using it to prevent cancer recurrence.
What if you accidentally took something risky?
If you realize you’ve taken a dangerous combo-like fluoxetine and terbinafine-don’t panic. But don’t wait either. Call your doctor or poison control immediately (1-800-222-1222 in the U.S.).
Symptoms to watch for:
- Rapid heartbeat or palpitations
- Confusion, agitation, or hallucinations
- High fever or sweating
- Shivering or muscle rigidity
- Seizures
These could be signs of serotonin syndrome or heart rhythm issues. Both need emergency care.
How to stay safe while taking terbinafine
Here’s a simple plan to avoid bad interactions:
- Make a full list of every medication you take-prescription, OTC, vitamins, herbs. Include doses and how often you take them.
- Bring that list to your pharmacist when you pick up terbinafine. Pharmacists are trained to catch drug interactions. They’ll flag the risky ones before you even leave the store.
- Ask your doctor if you can switch to a different antifungal. Itraconazole or fluconazole might be safer if you’re on multiple interacting drugs.
- Get a baseline liver function test before starting terbinafine. Repeat it after 6 weeks. If enzymes rise, stop the drug.
- Don’t start any new meds-even supplements-without checking with your provider.
Most people take terbinafine without issues. But the ones who get hurt? Usually didn’t tell their doctor everything they were taking. That’s the biggest mistake.
Alternatives to terbinafine
If you’re on a drug that can’t be mixed with terbinafine, there are other options:
- Fluconazole: Works for nail fungus and yeast infections. Less liver interaction, but takes longer to work.
- Itraconazole: Stronger than terbinafine for some fungal types. Still has interactions, but fewer with antidepressants.
- Laser treatment: For nail fungus, some clinics offer laser therapy. It’s expensive and not covered by insurance, but it’s drug-free.
- Topical antifungals: Ciclopirox or efinaconazole nail lacquers. Slower, but safe if you’re on multiple oral meds.
None of these are perfect. But if you’re on a beta-blocker or an SSRI, avoiding terbinafine might be the safest choice.
Can I take terbinafine with ibuprofen?
Low-dose ibuprofen (200-400 mg daily) is usually safe with terbinafine. But if you’re over 65, have kidney disease, or take it daily for arthritis, the risk of stomach bleeding or fluid retention increases. Talk to your doctor before combining them.
Does terbinafine affect blood pressure meds?
Yes. Terbinafine can increase levels of beta-blockers like metoprolol and propranolol by up to 60%. This can cause dangerously low heart rate or blood pressure. If you’re on one of these, your doctor should monitor your vitals closely or switch you to a different antifungal.
Is it safe to drink alcohol while taking terbinafine?
No alcohol is recommended. Both terbinafine and alcohol are processed by the liver. Drinking increases your risk of liver damage, even if you’ve never had liver problems. One glass occasionally might be okay, but daily drinking is dangerous.
How long do terbinafine interactions last after stopping?
Terbinafine stays in your system for weeks after your last dose. It can still block liver enzymes for up to 3-4 weeks. Don’t start any interacting drugs until at least a month after finishing terbinafine. Your pharmacist can help time it right.
What should I do if I miss a dose of terbinafine?
Take it as soon as you remember. If it’s almost time for your next dose, skip the missed one. Don’t double up. Missing doses won’t cause dangerous interactions, but it can make the antifungal less effective, leading to a relapse of the infection.
Final advice: Know your meds
Terbinafine works well. But it’s not harmless. The real danger isn’t the fungus-it’s the other pills you’re taking without realizing they clash. Always tell your doctor and pharmacist about every drug, supplement, and even occasional OTC medicine you use. If you’re on antidepressants, heart meds, or painkillers, don’t assume terbinafine is safe just because it’s common. Ask. Double-check. Save yourself from a preventable hospital visit.
