I en klinisk undersøgelse varierede den månedlige prevalens af symptomer af mindst moderat sværhedsgrad fra nervesystemet mellem uge 4 og 48, mellem 5 - 9% hos patienter i behandlingsregimer med efavirenz og mellem 3 - 5% hos patienterne, som fik kontrolbehandling.
In one clinical study, the monthly prevalence of nervous system symptoms of at least moderate severity between weeks 4 and 48, ranged from 5% - 9% in patients treated with regimens containing efavirenz and 3% - 5% in patients treated with the control regimen.