Ridged Nails: Drugs That Cause or Treat Them

Vertical vs. Horizontal Ridges: Why the Distinction Matters

The first clinical question is direction. Vertical ridges run from cuticle to tip and are called onychorrhexis. Horizontal ridges cross the nail side to side and are called Beau's lines. These two patterns have entirely different clinical significance, and confusing them leads to unnecessary anxiety or, worse, missed diagnoses.

Vertical ridges become nearly universal with aging. A cross-sectional survey published in the Journal of the European Academy of Dermatology and Venereology found that longitudinal ridging was present in over 60% of adults older than 40 and in more than 85% of those older than 70 [1]. The nail matrix gradually loses its smooth contour as cell turnover slows, producing the grooves most people notice in their 30s or 40s. No treatment is required for isolated vertical ridging in an otherwise healthy person.

Beau's lines tell a different story. First described by French physician Joseph Honoré Simon Beau in 1846, these transverse depressions mark a period when the nail matrix temporarily stopped producing cells. Each line is a timestamp. By measuring its distance from the cuticle and dividing by the average nail growth rate of 3.5 mm per month [2], a clinician can estimate when the insult occurred. Fever, major surgery, severe infection, chemotherapy, and nutritional collapse are classic triggers. A single Beau's line on one nail may follow local trauma. Beau's lines on all 20 nails point to a systemic event.

Drugs That Cause Nail Ridging

Medication-induced nail changes are more common than most patients realize. A 2003 review in Dermatologic Clinics cataloged over 30 drug classes capable of producing nail dystrophy [3], with ridging, discoloration, and onycholysis among the most frequent presentations.

Chemotherapy agents are the leading pharmaceutical cause. Taxanes (docetaxel, paclitaxel) and fluoropyrimidines (5-fluorouracil, capecitabine) routinely produce Beau's lines because they target rapidly dividing cells, and the nail matrix divides quickly. A prospective study of 58 patients receiving docetaxel found that 88% developed nail changes by cycle 4 [4], including transverse ridging, onycholysis, and subungual hemorrhage. These changes typically resolve 6 to 12 months after treatment ends, though nails may never fully return to their pre-treatment appearance.

Retinoids (isotretinoin, acitretin) thin the nail plate and disrupt keratinization. Patients on isotretinoin for acne frequently report brittle, ridged nails within the first 8 weeks. The mechanism involves altered lipid composition in the nail plate, reducing its structural integrity. A retrospective analysis in the British Journal of Dermatology documented nail fragility in 18 to 44% of patients on oral retinoid therapy [5].

Anticonvulsants, particularly valproic acid and carbamazepine, disrupt zinc and biotin metabolism. Valproic acid competes with biotin for intestinal absorption and depletes biotinidase activity. The resulting functional biotin deficiency can produce horizontal ridging, hair thinning, and perioral dermatitis. A case series published in Seizure reported nail dystrophy in approximately 10% of pediatric patients on long-term valproic acid [6].

Antiretrovirals, especially older nucleoside reverse transcriptase inhibitors (zidovudine, stavudine), cause nail hyperpigmentation and ridging through mitochondrial toxicity in the nail matrix. While newer regimens (tenofovir alafenamide, integrase inhibitors) carry lower nail toxicity, providers should still screen for nail changes at routine visits.

Other notable culprits include lithium, beta-blockers (particularly propranolol at high doses), and antimalarials (hydroxychloroquine). Each of these can impair nail matrix function through different pathways, including reduced peripheral blood flow, altered calcium signaling, or direct cytotoxicity.

Medical Conditions Behind the Ridges

Drug-induced ridging accounts for only a fraction of cases. Systemic disease is the other major driver, and several conditions overlap with the telehealth populations HealthRX serves.

Thyroid dysfunction ranks among the most clinically significant causes. Both hypothyroidism and hyperthyroidism alter nail growth. Hypothyroidism slows matrix turnover, producing thick, brittle nails with prominent vertical ridges. Hyperthyroidism accelerates turnover unevenly, causing soft, thin nails with Plummer's nails (onycholysis from the distal edge). The American Thyroid Association estimates that roughly 20 million Americans have some form of thyroid disease [7], making this a high-yield diagnostic consideration.

Iron deficiency is the most common nutritional cause globally. Ferritin levels below 30 ng/mL correlate with brittle nail syndrome, which includes ridging, splitting, and koilonychia (spoon-shaped nails). A 2019 study in the Indian Dermatology Online Journal found that patients with brittle nails had significantly lower serum ferritin compared to controls (mean 22.1 vs. 58.4 ng/mL, P<0.001) [8]. Correcting iron stores to a ferritin target above 50 ng/mL typically improves nail quality within two full growth cycles (8 to 12 months for fingernails).

Zinc deficiency produces a distinctive pattern of Beau's lines with white spots (leukonychia punctata). Zinc is a cofactor for over 300 enzymes involved in cell division, and the nail matrix is exquisitely sensitive to zinc depletion. Patients on proton pump inhibitors, those with inflammatory bowel disease, and individuals on restrictive diets face elevated risk.

Psoriasis affects nails in approximately 50% of patients with skin disease and up to 80% of those with psoriatic arthritis [9]. Nail pitting (small, punched-out depressions) is the hallmark, but longitudinal ridging and crumbling also occur when the nail matrix is involved. Distinguishing psoriatic nail changes from onychomycosis requires careful examination and sometimes biopsy or fungal culture.

Lichen planus of the nail matrix produces characteristic thinning, ridging, and, in severe cases, permanent scarring (pterygium). Early recognition and treatment with intralesional corticosteroids or systemic immunosuppression can prevent irreversible nail loss. Dr. Antonella Tosti, a professor of dermatology at the University of Miami and a leading authority on nail disorders, has written: "Nail lichen planus is a dermatologic emergency when it involves multiple nails, because delayed treatment leads to permanent nail destruction" [10].

Biotin: The Evidence for and Against

Biotin (vitamin B7) is the most widely marketed supplement for nail health. The data is modest but consistent.

The landmark study is a 1993 Swiss trial by Columbo and colleagues, who gave 2.5 mg of biotin daily to 35 patients with brittle nails. After a mean treatment duration of 5.5 months, nail thickness increased by 25% [11], and 63% of participants rated their nails as clinically improved. The study was small and uncontrolled, but it remains the most cited trial in this space. A follow-up study from the same group confirmed similar improvements in a larger cohort.

Several caveats apply. Biotin at high doses (5 to 10 mg) interferes with troponin, TSH, and other immunoassays that use streptavidin-biotin chemistry. The FDA issued a safety communication in 2017 [12] warning that biotin supplementation had caused at least one death due to a falsely low troponin result masking a myocardial infarction. Patients should stop biotin supplements at least 72 hours before blood draws. The 2.5 mg dose used in nail studies is lower than some commercial formulations (which may contain 5 to 10 mg), but even 2.5 mg can affect sensitive assays.

For patients with documented biotin deficiency (rare outside of genetic biotinidase deficiency or long-term anticonvulsant use), supplementation is clearly indicated. For patients with normal biotin levels and age-related vertical ridging, the evidence supports a trial of 2.5 mg daily for 6 months, with the understanding that the expected benefit is modest and the main risk is lab interference.

Other Treatments With Clinical Support

Beyond biotin, several interventions address specific causes of nail ridging.

Thyroid hormone replacement (levothyroxine for hypothyroidism) normalizes nail growth within 6 to 12 months of achieving euthyroid status. TSH should be the initial screening test for any patient presenting with new-onset nail changes alongside fatigue, weight changes, or hair thinning.

Iron supplementation targets ferritin levels above 50 ng/mL. Oral ferrous sulfate (325 mg, providing 65 mg elemental iron) taken every other day maximizes fractional absorption based on hepcidin cycling, as demonstrated in a 2017 randomized trial in Blood [13]. Intravenous iron (ferric carboxymaltose) may be necessary for patients with malabsorption.

Antifungal therapy applies when onychomycosis mimics or coexists with ridging. Terbinafine 250 mg daily for 12 weeks achieves mycologic cure rates of 70 to 80% [14] for dermatophyte infections of the fingernails. Fungal culture or PCR testing should precede treatment to confirm the diagnosis.

Topical corticosteroids and intralesional triamcinolone are first-line for nail psoriasis and lichen planus affecting the matrix. Clobetasol propionate 0.05% applied under occlusion nightly for 3 to 6 months has shown improvement in pitting and ridging scores in small controlled trials.

Drug substitution is the definitive treatment when medication is the identified cause. Switching from valproic acid to levetiracetam, or from isotretinoin to a topical retinoid, eliminates the offending stimulus. Nail changes typically take 4 to 9 months to grow out after the drug is stopped.

Dr. Richard Scher, former professor of dermatology at Columbia University and a founder of the Nail Society, noted in his clinical textbook: "The nail is a mirror of internal disease. Any unexplained change in nail morphology deserves at minimum a CBC, ferritin, zinc, and thyroid panel" [15].

The Diagnostic Workup: What Labs to Order

A patient presenting with ridged nails does not always need testing. Isolated vertical ridging in a person over 40 with no other symptoms warrants reassurance alone. Testing becomes necessary when horizontal ridges appear on multiple nails, when ridging is accompanied by other symptoms (fatigue, hair loss, weight changes), or when ridging develops abruptly in a younger patient.

The minimum panel includes TSH, free T4, ferritin, CBC with differential, and zinc. Expanding to include vitamin D (25-hydroxyvitamin D), B12, and folate is reasonable when nutritional deficiency is suspected. A medication history is as important as any lab, as patients often do not connect nail changes with their prescriptions.

Dermatologic referral is appropriate when nail biopsy is needed to rule out psoriasis, lichen planus, or melanonychia (pigmented nail streaks that can indicate subungual melanoma). Fungal culture or nail clipping for PAS staining should precede empiric antifungal therapy.

Nail dermoscopy (onychoscopy) is an emerging tool that allows non-invasive visualization of nail plate and nail bed abnormalities. The technique can differentiate traumatic onycholysis from psoriatic onycholysis, and it can detect early melanonychia patterns that warrant biopsy. Access to onychoscopy remains limited to specialized nail clinics, but its adoption is growing.

When Ridged Nails Signal Something Serious

Most nail ridging is benign. A small subset of presentations demands urgent attention.

Multiple Beau's lines across all nails suggest a severe systemic insult: sepsis, Kawasaki disease in children, high-dose chemotherapy, or acute renal failure. A study in Archives of Dermatology found that Beau's lines were present in 68% of patients admitted to the ICU for more than 2 weeks [16].

Longitudinal melanonychia (a dark streak running the length of the nail) may indicate subungual melanoma. While benign causes (ethnic pigmentation, trauma, medication) are more common, any new single-digit melanonychia in a light-skinned adult requires dermatology referral within 2 weeks. Hutchinson's sign (pigment extending to the proximal nail fold) raises the index of suspicion further.

Nail clubbing (increased curvature of the nail with loss of the normal angle between nail and nail fold) accompanies pulmonary fibrosis, lung cancer, inflammatory bowel disease, and congenital heart disease. This is distinct from ridging but occasionally confused with it. The Schamroth window test (placing opposing fingernails together to look for a diamond-shaped gap) is a simple bedside screen.

Rapid onset of nail brittleness, ridging, and hair loss together should prompt evaluation for autoimmune thyroiditis, iron deficiency anemia, or systemic lupus erythematosus. The overlap of these findings narrows the differential substantially and directs targeted testing.

Patients on GLP-1 receptor agonists (semaglutide, tirzepatide) who develop nail changes during treatment should be evaluated for nutritional deficiency, since rapid weight loss can deplete zinc, iron, and protein stores. A post-hoc analysis of the STEP trials noted that micronutrient deficiencies were not systematically tracked [17], leaving a gap in our understanding of nail and hair effects during GLP-1-mediated weight loss.