Metformin is a widely prescribed oral medication belonging to the biguanide class of drugs, primarily used as a first-line treatment for Type 2 diabetes. It works by reducing the amount of glucose the liver produces and by improving the body’s sensitivity to insulin, which helps to lower blood sugar levels. Tinnitus, often described as a ringing, buzzing, hissing, or roaring sound in the ears, is the perception of noise when no external sound is present. This phantom noise is a common symptom affecting a significant portion of the population. Patients are concerned about a potential link between this medication and the onset of this auditory symptom.
Examining the Reported Association
Metformin is not typically classified among the primary ototoxic medications—drugs known to cause hearing-related side effects—in the same way that certain antibiotics or chemotherapy agents are. Despite this, reports suggesting an association between Metformin use and tinnitus have surfaced through post-marketing surveillance systems. The FDA Adverse Event Reporting System (FAERS), for example, includes reports of hearing disorders, including tinnitus, associated with the drug, though these reports do not definitively prove causation.
The existence of an adverse event report indicates a correlation observed in a real-world setting, not necessarily a direct causal relationship. Reports related to hearing impairment exist in the pharmacovigilance data. However, the overall prevalence remains rare or infrequent compared to common side effects like gastrointestinal upset. Furthermore, large-scale studies investigating the relationship between Metformin and hearing loss have sometimes shown that Metformin users had a slightly lower, or at least a non-significantly different, risk of hearing loss compared to non-users.
Potential Physiological Explanations
The most commonly hypothesized biological pathway linking Metformin to auditory symptoms involves its established relationship with Vitamin B12. Metformin is known to interfere with the absorption of Vitamin B12 in the small intestine, and long-term use, particularly at higher doses, can lead to a deficiency in this vitamin. Vitamin B12 is crucial for the health and integrity of the nervous system, playing a fundamental role in the formation and maintenance of the myelin sheath that insulates nerve fibers.
A deficiency in B12 can therefore lead to peripheral neuropathy, which is damage to the peripheral nerves. This neurological damage can sometimes manifest as tinnitus or hearing loss. The cochlear nerve, which transmits sound information from the inner ear to the brain, relies on healthy myelin. When B12 levels are low, the demyelination of these neurons can disrupt the normal transmission of auditory signals, potentially leading to the perception of phantom sounds.
A separate mechanism relates to the drug’s effect on blood sugar. Metformin works to lower glucose levels. While it rarely causes hypoglycemia (low blood sugar), severe changes in glucose concentration can affect the inner ear. The inner ear’s complex metabolic function is sensitive to changes in the body’s homeostasis, including blood glucose and insulin levels. Hypoglycemic episodes can cause a temporary metabolic imbalance that affects the cochlea, which may result in auditory symptoms like buzzing or ringing.
Patient Guidance and Monitoring
Patients who develop new or worsening tinnitus while taking Metformin should treat it as a symptom requiring prompt medical attention from their healthcare provider. It is important to discuss the symptom thoroughly, including its onset and characteristics, to determine if the medication is a contributing factor.
Testing for Vitamin B12 levels is a necessary step, especially for individuals on long-term or high-dose Metformin therapy, as deficiency is a recognized side effect that can mimic or cause neurological symptoms. If a B12 deficiency is confirmed, the physician may recommend corrective treatment, such as B12 supplementation, but the Metformin treatment is generally continued unless otherwise advised.
Patients should never attempt to adjust their Metformin dosage or stop taking the medication on their own, as this can lead to dangerously high blood sugar levels. Managing the perception of tinnitus can involve strategies like sound masking, which uses external noise to cover the internal ringing, or cognitive behavioral therapy (CBT), which helps patients reduce the distress caused by the sound.