it causes deafness!
The effect of quinine on outer hair cell shape, compliance and force - PubMed
Quinine intoxication causes a well-described syndrome that includes tinnitus, sensorineural hearing loss and vertigo. The pathophysiology of quinine's effects on hearing is unknown, but may include a peripheral component. The cochlear outer hair cell is known to be motile and to contribute force...
pubmed.ncbi.nlm.nih.gov