Here is an study showing how it was used internally.
1.The percentage of cures in aseries of twenty-six infected children treated with a suspension of gentian violet was 81 per cent. The corrected cure rate was 92.3 per cent.
2.The suspension of gentian violetwas well accepted and tolerated by all forty of the children who received the medication in this study.
3.The nausea and vomiting observedin some patients treated with the enteric-coated gentian violet tablets was not observed in these patients treated with the suspension of gentian violet. Since the nausea and vomiting observed in patients treated with the enteric-coated gentian violet tablets, coupled with the inability of young children to swallow the intact enteric-coated tablets, comprise the major disadvantages in the treatment of enterobiasis with the enteric-coated gentian violet tablets, it appears from this study that the suspension of gentian violet is a more disirable method of treatment than the enteric-coated gentian violet tablets.
This 2013 study claims it has ANTI-cancer activity :