The Effects of Chronic Substance Misuse on the Auditory and Vestibular Systems: Preliminary Findings.

The study was a small pilot, with 60 substance misuse participants and 20 controls, and the authors say it was not large enough to account for all health, environmental, and social factors. Extended high-frequency thresholds were unusually sensitive at 16 kHz in both groups, and the authors are still checking whether this was a technical issue, so extended high-frequency conclusions are uncertain. Most participants reported polysubstance use, and the study did not stratify outcomes by specific substance, so the effect of one drug cannot be separated from the others. Substance use history was based on self-report, with no blood or urine testing, so some participants may have been intoxicated or withdrawing without visible impairment. Most participants were actively using rather than in recovery, so the study does not show how hearing or vestibular function changes during stable recovery. The substance misuse group had more health comorbidities, head trauma, smoking, and noise exposure than controls, and although head trauma, smoking, and noise exposure were adjusted for in some analyses, the study could not rule out other confounders. Caloric and rotary chair testing were not done, so low-frequency peripheral vestibular function was not fully assessed. Cervical VEMP amplitudes were not normalised for sternocleidomastoid muscle contraction, and the paper says this makes the cVEMP amplitude finding uncertain. Participants aged 60 and older were excluded, so results do not apply to older adults with age-related hearing or vestibular decline. Monocular eye recording may have introduced direction bias in saccade testing.

Do not read this as proof that chronic substance misuse causes classic extended high-frequency ototoxic hearing loss. The hearing difference was not specific to the extended high-frequency range, and the extended high-frequency thresholds were unusual and still under technical investigation.