Filgotinib Effects on Semen and Sex Hormones The oral Janus kinase 1 inhibitor filgotinib is available worldwide, but not in the USA, where the FDA held up its approval for use in RA due to unfinished studies of filgotinib's effects on sperm cells. https://t.co/SrwInSY45G https://t.co/TD54PXNFbi