Desuden medfører hydroxycarbamid en direkte hæmning af DNA- syntesen ved at fungere som en hæmmer af ribonukleotidreduktase uden at forstyrre syntesen for ribonukleinsyre eller - protein.
In addition hydroxycarbamide causes an immediate inhibition of DNA synthesis by acting as a ribonucleotide reductase inhibitor, without interfering with the synthesis of ribonucleic acid or protein.