Terbinafine is an antifungal medication used to treat pityriasis versicolor, fungal nail infections, and ringworm including jock itch and athlete's foot.

[5] Common side effects when taken by mouth include nausea, diarrhea, headache, cough, rash, and elevated liver enzymes.

[11] Tablets by mouth are often prescribed for the treatment of onychomycosis, a fungal nail infection, typically by a dermatophyte or Candida species.

[12] Many side effects and adverse drug reactions have been reported with oral terbinafine hydrochloride,[13][14] possibly due to its extensive biodistribution and the often extended durations involved in antifungal treatment (longer than two months).

A comprehensive list of adverse events associated with terbinafine use includes: In 2015, physicians reported[16] that a patient with an MTHFR enzyme mutation (specifically the C677T variant) had developed an adverse reaction to terbinafine (Lamisil) (headache, fatigue, and dizziness).

It was noted that Lamisil interferes with the methylation cycle and that this can cause side effects in individuals with the MTHFR C677T mutation.

However, as fungi and animals diverged around 1.1 billion years ago - there is enough difference in this enzyme that terbinafine preferentially binds fungal squalene epoxidase, making it selective for inhibiting ergosterol production in fungi without significantly affecting cholesterol production in mammals.

[citation needed] Terbinafine is highly lipophilic and tends to accumulate in hair, skin, nails, and fat cells.

The U.S. Food and Drug Administration has approved the first generic versions of prescription Lamisil (terbinafine hydrochloride) tablets.