Lamisil (terbinafine): uses, dosage, side effects and refills

Terbinafine is an allylamine antifungal, chemically different from the azoles such as fluconazole. Its oral tablet is the standard prescription for fungal nail infection, known medically as onychomycosis or tinea unguium, when it is caused by dermatophytes such as Trichophyton rubrum and T. mentagrophytes (terbinafine label, 1 and 12.4).

What makes it suited to nails is where it goes. More than 70% of an oral dose is absorbed, it binds over 99% to plasma proteins, and it concentrates in skin, sebum and fat. The effective half-life is about 36 hours, but a terminal half-life of 200 to 400 hours reflects slow release from skin and fatty tissue (label, 12.3). Drug therefore keeps acting in the nail bed long after the course ends.

It was first sold as Lamisil; DailyMed now lists oral terbinafine under generic labels, while Lamisil AT cream and spray are sold without a prescription for athlete's foot and similar skin infections. Terbinafine was No. 258 among US prescriptions in 2024, about 1.4 million fills (ClinCalc DrugStats).

FDA-labeled use of the tablets (terbinafine label, section 1): treatment of onychomycosis of the toenail or fingernail due to dermatophytes (tinea unguium).

The label asks prescribers to confirm the diagnosis first with a nail sample: a potassium hydroxide (KOH) preparation, a fungal culture or a nail biopsy. That matters because psoriasis, trauma and non-dermatophyte molds can look like nail fungus and will not respond.

What the trials showed (label, section 14):

• First toenail trial, 12 weeks of treatment then 36 weeks of follow-up: 70% reached mycological cure (negative KOH and culture), 59% had effective treatment, and 38% had both mycological cure and a completely clear nail.
• Fingernail trial, 6 weeks then 18 weeks of follow-up: 79% mycological cure, 75% effective treatment, 59% complete cure.
• Median time to overall success was about 10 months for toenails and 4 months for fingernails, because the healthy nail has to grow out. Among toenail patients followed long enough, clinical relapse was about 15%.

Other forms: MedlinePlus lists terbinafine granules for fungal infection of the scalp. Topical terbinafine 1% (Lamisil AT) is used without a prescription for athlete's foot, jock itch and ringworm of the skin, which do not usually need tablets.

Not for yeast: terbinafine's lab activity against Candida albicans has not been shown to translate into clinical benefit, so it is not used for thrush or vaginal yeast (label, 12.4).

Fungi make ergosterol, their equivalent of cholesterol, through a chain of enzymes. Terbinafine blocks an early one, squalene epoxidase. Two things follow: the fungus runs short of ergosterol, and squalene accumulates to toxic levels inside the cell. The label notes that cell death is driven mainly by the squalene build-up, which makes the membrane leaky, rather than by the ergosterol shortage (terbinafine label, 12.4). That is why terbinafine can be fungicidal, killing dermatophytes rather than just stopping their growth.

Terbinafine reaches the nail through the nail bed and matrix and persists there. The new nail that grows out is free of infection, which is why visible improvement lags months behind the end of treatment.

In the liver, at least seven CYP enzymes break terbinafine down, chiefly CYP2C9, CYP1A2, CYP3A4, CYP2C8 and CYP2C19. Terbinafine itself strongly inhibits CYP2D6, the enzyme behind most of its drug interactions.

Do not take terbinafine tablets if you have chronic or active liver disease, or if you have had an allergic reaction to oral terbinafine, because of the risk of anaphylaxis (terbinafine label, section 4).

Before the first dose, the label asks prescribers to check for liver disease and to obtain liver function tests (serum transaminases), since liver failure has occurred in people with and without prior liver disease.

Tell your prescriber about:

• Any liver condition, heavy drinking or hepatitis.
• Kidney impairment. Use at a creatinine clearance of 50 mL/min or less has not been adequately studied, and clearance falls by about half.
• Depression or anxiety. Depressive symptoms are reported during treatment.
• Lupus, which terbinafine can trigger or worsen.
• A weakened immune system. Blood counts may be checked if treatment runs beyond 6 weeks.
• Medicines processed by CYP2D6, including many antidepressants, beta blockers and flecainide.
• Warfarin, cyclosporine, rifampin or caffeine use.
• Pregnancy or breastfeeding.

Ask your prescriber: Has my nail fungus been confirmed by a lab test, and when will my liver be rechecked?

One 250 mg tablet daily is the whole regimen; a consistent time of day helps, and meals are optional because food raises absorption by less than 20%, which does not matter clinically (terbinafine label, 7.2).

Course length: 6 weeks for fingernails and 12 weeks for toenails. Finish the full course even though the nail will still look infected when you stop. The label explains that the best result appears some months after cure, once healthy nail has grown out.

Expect slow visible progress. In trials, toenails took a median of about 10 months to reach overall success.

Know the warning signs before you start. The label asks patients to report right away persistent nausea, loss of appetite, tiredness, vomiting, upper-right belly pain, yellow skin or eyes, dark urine or pale stools, and to stop the tablets if these appear.

Report taste or smell changes promptly. The label says to stop if they occur, because they can be prolonged or permanent.

Granules (for scalp infection, per MedlinePlus) are sprinkled on a spoonful of non-fruit soft food such as pudding or mashed potatoes and swallowed without chewing.

Keep follow-up appointments for liver tests during treatment.

There is only one tablet dose. Every adult with labeled onychomycosis takes 250 mg once daily; only the course length differs by nail. Taking more does not speed results.

Liver monitoring is required: liver function tests before starting and periodically during treatment, with the tablets stopped if biochemical or clinical evidence of liver injury appears (label, 5.1).

Blood counts may be checked in people with known or suspected immune deficiency if treatment continues beyond 6 weeks, and the drug is stopped if neutrophils fall to 1,000 cells/mm3 or below (label, 5.5).

Older adults: trials had too few people 65 and over to show differences, so the label suggests caution given more frequent liver, kidney and heart disease.

Kidney or liver impairment roughly halves clearance; use with CrCl of 50 mL/min or less is not well studied.

Your prescriber decides whether tablets suit you and how you will be monitored.

Take a missed tablet when you remember. If your next tablet is due in less than 4 hours, skip the missed one and go on as normal; do not take two to make up (MedlinePlus). An occasional missed day does not ruin a 12-week course, but steady daily doses keep enough drug building up in the nail.

Doses of up to 5 grams, 20 times the daily dose, have been taken without serious reactions. Reported symptoms were nausea, vomiting, abdominal pain, dizziness, rash, frequent urination and headache (terbinafine label, section 10). After an accidental extra handful of tablets, Poison Help (1-800-222-1222) can tell you what to watch for. Call 911 if someone collapses, has trouble breathing or cannot be woken.

• Alcohol in excess and other liver-stressing substances during the course; the label contraindicates terbinafine in active liver disease.
• Ignoring liver warning signs: persistent nausea, poor appetite, fatigue, dark urine, pale stools or yellowing mean stop and call.
• Pushing on through taste or smell loss; the label says stop, because the change can become permanent.
• Large amounts of caffeine, since terbinafine slows caffeine clearance by 19%.
• Strong sun exposure without protection; photosensitivity reactions are reported.
• Starting another CYP2D6-processed drug, such as many antidepressants or beta blockers, without asking a pharmacist, for at least a month after finishing.
• Expecting fast results; stopping early because the nail still looks bad wastes the course.

Pregnancy: postmarketing data are insufficient to judge the risk of birth defects or miscarriage. Animal studies at 12 to 23 times the human dose showed no malformations or fetal harm (terbinafine label, 8.1). Nail fungus is rarely urgent, so ask your prescriber whether treatment can wait until after pregnancy.

Breastfeeding: terbinafine passes into human milk after oral doses, and effects on a nursing infant or on milk supply are unknown (label, 8.2). The label asks the prescriber to weigh the benefit of breastfeeding against the mother's need for treatment. Topical options or waiting until weaning are questions to raise.

Store terbinafine tablets at 68°F to 77°F, protected from light, with brief temperature excursions between 59°F and 86°F permitted (terbinafine label, 16). Keep them in the child-resistant bottle, away from moisture, and out of the reach of children.

Generic terbinafine is among the cheapest prescription antifungals. Cost Plus Drugs prices, with its $5 fee already counted and $5.25 standard shipping extra (costplusdrugs.com, checked 6 Oct 2026):

A 12-week toenail course is 84 tablets, so the 90-count at $12.70 covers it; a 6-week fingernail course fits in 60 at $10.13. Liver blood tests before and during treatment are a separate cost. Most drug plans cover generic terbinafine. Temi does not add to what your pharmacy charges for terbinafine (usetemi.com/about, checked 6 Oct 2026).

• Ciclopirox: a topical nail lacquer for mild to moderate nail fungus, without liver monitoring.
• Fluconazole: an azole tablet aimed mainly at yeast infections rather than dermatophyte nail fungus.
• Clotrimazole: a topical azole for athlete's foot and skin fungus.
• Ketoconazole: topical azole used for skin and scalp fungal conditions.
• Clotrimazole and betamethasone: an antifungal-steroid cream for inflamed skin fungal rashes.

As a non-scheduled antifungal, terbinafine is within what Temi physicians review online. Continuing a current prescription is a $15 refill review, or no charge for Temi Care members (usetemi.com/prescription/refills, checked 6 Oct 2026); a new course is a $79 one-off review (usetemi.com/get-prescribed, checked 6 Oct 2026). Because the label requires liver tests before starting and a confirmed nail diagnosis, be ready to share recent results or arrange them locally. If approved, the prescription goes to your pharmacy, usually within 48 hours.