Many medications are ototoxic, meaning that they adversely affect inner ear function. The toxicity can be divided into two broad categories, cochleotoxicity and vestibulotoxicity. Cochleotoxic medications affect hearing function and typically manifest with tinnitus (an abnormal noise in the ear), decreased hearing, or both. Most cochleotoxins affect hearing at the highest frequencies first, reflecting damage to hair cells of the cochlea. Vestibulotoxic medications affect the part of the inner ear that senses motion—the vestibular system. Vestibulotoxicity usually manifests with dizziness, unsteadiness, and when severe, oscillopsia. Oscillopsia denotes inability of a person to see when the head is moving, although visual acuity may be normal when the head is still. The most common vestibulotoxins, the aminoglycoside antibiotics, primarily damage the vestibular hair cells. Ototoxicity is often irreversible, as humans lack the ability to regenerate hair cells.

Ototoxic medications can be broken down into several broad groups. Chemotherapeutic agents are often cochleotoxic. Many antibiotics are ototoxic, and those in the aminoglycoside family are all ototoxic to some degree, some being primarily cochleotoxic and others primarily vestibulotoxic. Diuretics, mainly the loop diuretics, are often cochleotoxic. Similarly, quinine derivatives such as antimalarials are also commonly cochleotoxic. Many common medications in the nonsteroidal anti-inflammatory group, such as aspirin, are cochletoxic.