The patient first came to the adult sleep medicine clinic complaining of severe excessive daytime sleepiness. Her medical history was complex: she had been diagnosed with multiple sclerosis at the age of 15, previously managed with monthly interferon injections that she had discontinued without relapses. More significantly, at age 14 she had been found to have a pituitary microadenoma measuring between 6 and 9 millimeters after an episode of vaginal bleeding. At that time she was also diagnosed with hyperprolactinemia, an excess of the hormone prolactin, and was treated with cabergoline and oral contraceptive pills for one year. She had stopped the contraceptive pills two years before her sleep clinic visit and had experienced no vaginal bleeding since.

At the sleep clinic, her Epworth Sleepiness Scale score was 20, indicating severe daytime sleepiness, but she had no cataplexy, hallucinations, or sleep paralysis. Overnight polysomnography showed a sleep latency of 12 minutes, an apnea-hypopnea index of 0.0, and sleep efficiency of 90.5 percent over six hours of total sleep time. Multiple sleep latency testing demonstrated a mean sleep latency of just 2 minutes and 48 seconds, with two sleep-onset REM periods and an average REM latency of 3 minutes. In the absence of cataplexy, these findings were consistent with a diagnosis of narcolepsy type 2, the form of the disorder whose underlying cause remains unclear.

Modafinil was initiated at a dose of 100 milligrams twice daily. Within two to three days, coinciding with the start of menstruation, the patient noticed vaginal bleeding that persisted beyond the usual seven-day duration. The bleeding was mild at first and confined to a single source, with no bleeding from any other site. She was not taking any medication known to cause or worsen bleeding, such as aspirin or omega-3 supplements. Over the following month the bleeding worsened, and she received tranexamic acid intravenously and orally for four days without improvement. The decision was made to stop modafinil, and eleven days later the bleeding stopped completely.

Given her history of pituitary microadenoma and hyperprolactinemia, the clinicians conducted a thorough hormonal workup during the bleeding episode. Her prolactin level was elevated at 40 micrograms per liter, although notably lower than the pre-treatment level of 119 micrograms per liter recorded before modafinil was started. Thyroid function tests and coagulation profile were within normal limits. Testosterone was 0.90 nanograms per deciliter, follicle-stimulating hormone was 4.80 milli-international units per milliliter, and luteinizing hormone was slightly low at 1.70 international units per liter. Pelvic ultrasound was unremarkable, and endometrial thickness was within the expected range. No structural, endocrine, or hematologic alternative cause for the bleeding could be identified.

Due to academic demands, the patient resumed modafinil, which again coincided with the start of menstruation and once more triggered vaginal bleeding. This time the bleeding persisted even after she stopped the medication and required emergency department treatment with intravenous and oral tranexamic acid for three days with no improvement. Her hemoglobin dropped to 6.6 grams per deciliter and iron deficiency was noted, although her platelet count remained normal at 390 × 10⁹ per liter. She required a blood transfusion and resumed oral contraceptive pills to control the bleeding.

As an alternative therapy for her narcolepsy, methylphenidate 18 milligrams daily was initiated ten days before menstruation was due. Within four days the patient developed spotting that did not progress to full vaginal bleeding; the spotting resolved spontaneously within a few days while she remained on treatment. Methylphenidate was discontinued after one week in accordance with the patient’s preference. The pattern across all three exposures, two with modafinil and one with methylphenidate, suggests a class effect of catecholaminergic stimulants on endometrial stability in a hormonally susceptible patient.

Narcolepsy is a chronic neurological disorder affecting approximately one in 2,000 people, characterized by an irresistible and sudden urge to sleep. Despite its relative frequency, diagnosis is often significantly delayed, typically taking between five and fifteen years, and up to half of affected individuals may remain undiagnosed. The condition is classified into two types: type 1 narcolepsy, associated with significant loss of hypothalamic neurons producing the neuropeptide hypocretin, also known as orexin, and type 2 narcolepsy, whose cause remains unclear. The five hallmark symptoms are excessive daytime sleepiness, cataplexy, sleep paralysis, hypnagogic hallucinations, and disrupted nocturnal sleep, with the presence of cataplexy strongly linked to hypocretin deficiency.

Modafinil acts by competitively binding to the dopamine transporter on cell membranes and relies on catecholaminergic signaling, both dopaminergic and adrenergic, for its wake-promoting effects. It is generally well tolerated, with headache, nausea, and infections being the most commonly reported side effects, and a lower risk of tolerance compared to methylphenidate. The American Academy of Sleep Medicine recommends modafinil as a first-line treatment for excessive sleepiness due to narcolepsy, with methylphenidate also effective for daytime sleepiness. The typical starting dose of modafinil is 200 milligrams once daily, usually in the morning, with split dosing regimens considered for persistent sleepiness.

Serious adverse effects of modafinil, though rare, have been documented. Severe skin reactions such as Stevens-Johnson syndrome and toxic epidermal necrolysis have been reported, including in a 40-year-old woman after three weeks of daily use, with histopathology confirming full-thickness epidermal necrosis and subepidermal blistering. Other serious effects include aggravation of psychotic symptoms in patients with schizophrenia, mania, and hallucinations, as reported in a 19-year-old who took modafinil to increase academic performance and presented to an emergency department five days later with psychotic symptoms. Cardiovascular issues such as chest pain and irregular heartbeats have also been described; in a retrospective review of 89 patients with supratherapeutic modafinil exposure, 23 patients, or 26.4 percent, experienced tachycardia with heart rates ranging from 101 to 168 beats per minute, although no major adverse cardiac events occurred and all patients recovered without sequelae.

Currently, there are no documented case reports in the medical literature that directly attribute bleeding to modafinil use, making this case one of the few reported instances linking wakefulness-promoting agents to significant gynecological bleeding. While the exact mechanism is unclear, the authors suggest that dopaminergic and adrenergic stimulation may have interacted with underlying hormonal imbalances, precipitating endometrial instability and bleeding. The patient’s history of pituitary microadenoma and prior hyperprolactinemia may have created a hormonal environment in which catecholaminergic stimulation destabilized the endometrium, though this remains speculative.

The case underscores the importance of close monitoring and individualized treatment strategies when prescribing stimulant medications, especially in patients with a history of hormonal disorders such as pituitary adenoma. Clinicians should be aware of the potential for vaginal bleeding in patients receiving these agents, and a careful medication history should be taken in any patient with unexplained gynecological bleeding who is taking wakefulness-promoting drugs. As modafinil continues to be prescribed widely and used off-label by healthy individuals seeking cognitive enhancement, this report serves as a reminder that even drugs considered safe and well tolerated can produce rare but significant adverse effects in vulnerable patients.

Subject of Research: Modafinil and abnormal bleeding in a young lady with narcolepsy: a case report

Article Title: Modafinil and abnormal bleeding in a young lady with narcolepsy: a case report

Article References: Rashed, A. N., Abdelbasit, A., & Alshahrani, M. (2026). Modafinil and abnormal bleeding in a young lady with narcolepsy: a case report. Frontiers in Drug Safety and Regulation, 6, Article 1767644. https://doi.org/10.3389/fdsfr.2026.1767644

Image Credits: AI Generated

DOI: 10.3389/fdsfr.2026.1767644

Keywords: modafinil, narcolepsy, drug safety, vaginal bleeding, methylphenidil, hyperprolactinemia, pituitary microadenoma, abnormal, bleeding, young, lady, case