Terbinafine: What It Treats, How to Use It, and Safety Tips

Terbinafine treats fungal infections of skin, hair and nails. You may know it as an effective option for athlete’s foot, ringworm, and toenail fungus. It comes as a cream, spray, or an oral tablet. Topical forms work locally and rarely cause side effects; oral terbinafine reaches deeper infections like nail fungus but has more risks.

How it works

Terbinafine blocks an enzyme fungi need to make their cell walls. That stops fungal growth and helps your immune system clear the infection. Because it targets fungi, it won’t help viral or bacterial skin problems.

Common uses and typical courses: For athlete’s foot and ringworm you’ll usually use a cream once or twice a day for one to four weeks depending on the spot and severity. For fingernail infections doctors often prescribe 250 mg daily for six weeks; for toenails the same dose for twelve weeks is common. Exact timing depends on the drug brand and your doctor’s judgment—follow their plan.

Side effects to watch for: Topical irritation, burning, or redness can happen with creams. Oral terbinafine can cause headache, nausea, stomach upset, and a taste or smell change. Rare but serious effects include liver injury and severe skin reactions. If you notice yellowing skin or eyes, dark urine, severe fatigue, persistent stomach pain, or a rash that spreads quickly, stop the medicine and contact a clinician right away.

Interactions and precautions: Oral terbinafine can interact with other drugs because it affects liver enzymes, especially CYP2D6. Tell your doctor about antidepressants, some blood pressure drugs, tamoxifen, and other prescription medicines. Avoid heavy alcohol use while on the oral form. People with active liver disease, kidney problems, or a known allergic reaction to terbinafine should not take it. Pregnant or breastfeeding people should discuss alternatives—oral terbinafine is generally avoided in pregnancy.

Practical tips for using terbinafine

Clean and dry the affected area before applying cream. Finish the full course even if symptoms improve early—fungus can hide and come back. For nail infections expect slow progress: nails grow slowly, and visible improvement may take months after the medicine stops. Use a separate towel and wash socks and shoes regularly to cut reinfection risk.

When to see a doctor: If infections keep coming back, spread, or don’t improve after the recommended course, book a medical review. Lab tests like liver function panels are sometimes ordered before and during long oral treatment.

You can store terbinafine at room temperature away from moisture and heat. If you miss an oral dose, take it as soon as you remember that day—don't double up the next day. For kids, topical forms are common; oral tablets are usually used in adults. Elderly people may need dose checks if they have liver or kidney issues. Always tell your provider about herbal supplements and over-the-counter meds before starting terbinafine. Talk to your doctor.