Abstract
Drug-induced black hairy tongue (BHT) is a rare dermatological condition characterized by hypertrophy of the filiform papillae on the dorsal surface of the tongue, resulting in hyperpigmented discoloration. While most cases are asymptomatic and identified incidentally, some patients experience itching, discomfort, altered taste sensation, and halitosis. 1 Even though blackish discoloration does not cause apparent harm, it can lead to discontinuation of prescribed medications, resulting in worsening of the primary condition. The most common drugs implicated in the development of BHT include psychotropics (such as olanzapine, chlorpromazine, and alprazolam), antibiotics (like linezolid), and antihypertensives (notably methyldopa). 2 Among these, psychotropics are particularly important because they are generally required for long-term use, and discontinuation carries a risk of relapse. Although isolated case reports exist, no comprehensive reviews on psychotropic medication-related BHT have been found. In this article, we review the existing literature on psychotropic medication-related BHT and present two cases of olanzapine-induced BHT along with their management. Written informed consent was obtained from both the patients and their guardians before reporting the case.
Case 1
A 16-year-old female adolescent, currently in 10th grade, from a rural lower-middle socioeconomic background, presented with a 20-day history of easy irritability, elevated mood, increased activity, pressured speech, and reduced sleep. She was also behaving aggressively over the preceding 3–4 days, necessitating physical restraint at home. The onset was abrupt, with a continuous worsening course. Due to the risk of harm to self and others, inpatient management was initiated.
Mental Status Examination (MSE) on admission revealed increased psychomotor activity, irritable affect, pressured speech with grandiose delusions, impaired attention, and judgment. A diagnosis of bipolar type I disorder, current manic episode, with psychotic symptoms, was made according to the International Classification of Diseases-11th Revision (ICD-11). 3 She had a history of hypothyroidism for which she was receiving daily supplementation with 25 mcg of thyroxine. The baseline complete blood count, liver, and kidney function tests, serum electrolytes, thyroid function tests, and brain Computed Tomography (CT) scan were all within normal limits.
After initial stabilization with injectable haloperidol (10 mg) and promethazine (50 mg) for two days, the patient was started on oxcarbazepine (600 mg), olanzapine (5 mg), and lorazepam (6 mg). Oxcarbazepine was increased to 900 mg after five days, while lorazepam was tapered over a 10-day period. Olanzapine was gradually titrated to 20 mg over a 15-day period. Two days after reaching the 20 mg olanzapine dose, her mother reported blackish tongue discoloration (Figure 1). Clinical examination revealed thick, black, hair-like filiform papillae on the dorsal tongue without taste alterations. The patient had no history of nicotine use or excessive caffeine intake, and oral hygiene was adequate. Dermatology consultation and scrape biopsy revealed possible drug-induced BHT, likely linked to olanzapine’s anticholinergic properties. The adverse reaction was reported to the Institute’s Pharmacovigilance Unit.
Literature review suggested a higher incidence of BHT with olanzapine compared to oxcarbazepine and lorazepam. The Naranjo Adverse Drug Reaction Probability Scale was applied, yielding a score of 7, indicating a probable drug-related cause. 4 Although the lesion was non-progressive and asymptomatic, the patient’s mother expressed concern, leading to a tapering of olanzapine to 10 mg over 10 days. Gentle tongue brushing was concurrently recommended. Following the dose reduction, the lesion gradually faded, with symptoms resolving completely within two weeks. The patient was discharged on oxcarbazepine 900 mg and olanzapine 10 mg. At the 15-day follow-up, she remained stable, and the BHT had fully resolved (Figure 1).
Top Left: Black Hairy Tongue (BHT) in Case 1 in Symptomatic Phase; Top Right: Improvement in BHT in Case 1 After Improvement; Bottom Left: BHT in Case 2 in Symptomatic Phase; Bottom Right: Improvement in BHT in Case 2 After Improvement.
Case 2
An 18-year-old female presented with an 18-day history of the abrupt onset of suspiciousness, irritability, episodes of unprovoked aggression, self-harming behavior, and poor self-care. One week prior to this consultation, she had been diagnosed with a manic episode. She was started on tablet divalproex sodium 1,000 mg and escalating doses of olanzapine (up to 10 mg) by a physician. Although her sleep and aggression somewhat improved with the medications, suspiciousness, self-muttering, and anger outbursts persisted. On presentation, general physical examination revealed self-inflicted wounds, including bruised and swollen lips, as well as bruises across the neck and left knee joint, sustained while being restrained by family members during a physically aggressive outburst. MSE revealed a dysphoric affect, pressured speech, thought broadcasting, delusions of persecution, and referential ideas, along with impaired judgment and insight. A revised diagnosis of acute and transient psychotic disorder, first episode, was made according to ICD-11 criteria. 3
Following admission, olanzapine was continued and gradually increased to 20 mg. Clonazepam 0.5 mg was added at night and prescribed on an as-needed (SOS) basis. Over the next 15 days, aggression and suspiciousness significantly decreased. Divalproex sodium was gradually tapered and discontinued due to a lack of clinical indication.
However, on the 15th day of admission, a blackish discoloration appeared on the dorsum of the tongue, which gradually worsened over the following week (Figure 1). A dermatology consultation was obtained, and investigations were performed to exclude fungal infection. A potassium hydroxide (KOH) mount was negative, and scrape examination revealed characteristic hypertrophied hyperpigmented papillae. Oral hygiene was ensured, and chlorhexidine mouthwash was prescribed thrice daily. The Naranjo Adverse Drug Reaction Probability Scale score was 6, indicating a probable association with olanzapine. 4 The adverse reaction was reported to the Institute’s Pharmacovigilance Unit. Due to her parents’ concern about the discoloration, olanzapine was tapered and discontinued. The patient was started on risperidone, initially 2 mg and gradually increased to 5 mg. Subsequently, she developed hyperprolactinemia and galactorrhoea (serum prolactin level: 125 ng/ml), along with extrapyramidal symptoms, for which trihexyphenidyl 2 mg was initiated. Quetiapine was then introduced and titrated up to 800 mg while cross-tapering risperidone. Over the next 14 days, the BHT gradually resolved. At one-month follow-up via teleconsultation, she was maintaining well, with the BHT completely resolved (Figure 1).
Both cases were appropriately referred and treated. No significant dysfunction occurred, and both had improved on follow-up.
Discussion
A search of the online databases PubMed, Google Scholar, and EBSCO was conducted for articles published between 2000 and 2025. Additionally, a hand search was conducted of the reference lists and citations of all retrieved articles. The search terms were “BHT,” “lingua villosa nigra,” “hairy tongue,” “antipsychotic,” “mood-stabilizer,” “anti-depressant,” “sedative-hypnotics,” “psychotropics,” “psychiatric,” “side effect,” and “adverse drug reaction.” Reports in which BHT was associated with any of the psychotropics or other medications commonly used by psychiatrists were collected. The full-text articles were retrieved, and duplicates were removed. Non-English articles for which we could not acquire a translation were excluded from the literature review. The case reports have been compiled in Table 1.
Case Reports of Psychotropic Medication-induced Black Hairy Tongue in the Existing Literature.
Literature search revealed case reports of a total of 13 patients who developed BHT with psychotropic medications. In the majority of cases (8 out of 13), the offending medication was olanzapine (61.5%). The average dose of olanzapine used in these cases was 15.7 mg. One of the eight cases did not mention the dose of olanzapine given. The duration of recovery from BHT in the cases ranged from 1 to 12 weeks. In three cases, rechallenge with olanzapine was attempted, which was associated with the recurrence of BHT. Naranjo’s adverse drug reaction probability was used in most of the cases. However, only a few cases were reported to any Pharmacovigilance Unit. In other cases, the offending agent was not rechallenged. None of the cases suffered significant issues with BHT except for cosmetic concerns.
The BHT is a benign, self-limiting condition characterized by abnormally hypertrophied and elongated filiform papillae on the dorsal surface of the tongue. The prevalence of BHT varies widely, ranging from 0% to 53.8%. 18 BHT is hypothesized to develop due to impaired desquamation on the dorsal surface of the tongue. This impaired desquamation prevents normal debridement, resulting in the accumulation of keratinized layers. The resulting hypertrophy and elongation of the filiform papillae give a hair-like appearance. Usually less than 1 mm in length, the elongated papillae can reach lengths of 12 mm–18 mm and widths of 2 mm. These papillae then collect fungi, bacteria, and debris secondarily. This collection may include residue from tobacco, coffee, tea, and other foods, as well as porphyrin-producing chromogenic organisms in the oral flora, which impart the tongue’s characteristic color. 19
Antibiotics and drugs with strong anticholinergic properties, such as olanzapine and chlorpromazine, are frequently associated with the development of BHT. Chlorpromazine, mepazine, and other phenothiazines have been implicated in the development of BHT. 20 The proposed mechanisms include alteration of the bacterial flora (dysbiosis) on the tongue surface and xerostomia caused by anticholinergic effects, which impairs normal desquamation and promotes hypertrophy of filiform papillae. 18 However, this association is not absolute; for example, in the second case that we reported, the patient developed BHT with olanzapine but not with quetiapine, despite both having anticholinergic properties.
A thorough history should assess oral and tongue hygiene as well as the use of tobacco, caffeinated drinks, and other staining foods. In the cases reported, oral hygiene was well maintained, and there was no history of tobacco or caffeine use, suggesting that the medication—particularly olanzapine—was the likely cause. This aligns with the literature indicating that olanzapine-induced anticholinergic xerostomia leads to defective desquamation and the accumulation of keratinized papillae, resulting in characteristic discoloration.
The BHT is primarily a clinical diagnosis based on characteristic observation of the tongue’s dorsal surface. In some cases, diagnostic confirmation may be supported by scrape biopsy, KOH mount, or microscopic examination to exclude fungal infections or other pathologies. 18 Recent initiation of known offending agents is often present; however, spontaneous occurrence of BHT has also been reported. Common differential diagnoses include malignant lesions, fungal infections, discoloration due to excessive tobacco or caffeine use, and chronic poor oral hygiene. 18
Management of psychotropic-induced BHT is usually conservative, as the condition is mostly self-limiting. Regular brushing of the tongue with a soft toothbrush is often sufficient to resolve mild cases of tongue irritation. In severe or persistent cases, dose reduction of the offending drug or switching to an alternative with lower xerostomic potential may be considered, balancing the risk of exacerbating the primary psychiatric condition. Oral retinoids or topical tretinoin have been used in some instances, but these treatments are rarely necessary. Maintaining good oral hygiene and addressing modifiable risk factors remain the cornerstone of management.
Although BHT is generally a benign and self-limiting condition, it often attracts attention due to its unusual cosmetic appearance. Even mild cases, which do not cause significant physical discomfort, can provoke considerable anxiety and concern among patients and caregivers. This heightened worry may lead to premature discontinuation of essential psychotropic medications, risking relapse or worsening of the underlying psychiatric disorder. Before a diagnosis of BHT is made, a thorough medical history is crucial to rule out other potential causes. A poignant case report described an older woman on long-term olanzapine therapy who developed BHT. 16 Although the condition did not interfere with swallowing or eating, she was stigmatized. She was derogatorily labeled a “black tongued witch” by her community, highlighting the social and psychological impact that the condition’s appearance can have.
While this case series is the first to incorporate a detailed narrative review of psychotropic-related BHT, the findings cannot be generalized to support any strong recommendation regarding any restriction in the usage of specific psychotropics.
Conclusions
The BHT is a rare, self-limiting clinical condition. Although it does not cause significant issues with taste sensation or swallowing, its unusual appearance often raises concern among patients and caregivers. Providing clear information about the benign and self-resolving nature of BHT is essential to alleviate anxiety. Management may include simple measures such as gentle brushing of the tongue, dose reduction of the offending medication, or switching to an alternative agent when appropriate.
Supplemental Material
Supplemental material for this article available online.
Footnotes
Declaration of Conflicting Interests
The authors declared no potential conflicts of interest with respect to the research, authorship, and/or publication of this article.
Declaration Regarding the Use of Generative AI
None used.
Funding
The authors received no financial support for the research, authorship, and/or publication of this article.
Patient Consent and Ethical Considerations
Written consent and assent was taken from the patients and their caregivers as applicable. Ethical Approval is not required.
Prior Presentations
This article has not been presented anywhere prior to submission.
Reporting Guidelines
The CARE guidelines (supplementary online material).
Simultaneous Submission to Another Journal or Resource
This article has not been sent in any journal simultaneously for consideration for publication.
Statement
The case series being submitted has not been published, simultaneously submitted, or already accepted for publication elsewhere. The manuscript has been read and approved by all the authors. The manuscript, to the best of the author’s knowledge, does not infringe upon any copyright or property right of any third party.
References
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