(4-Hydroxyphenoxy)acetic acid along with formaldehyde ammonium salt forms a polyaromatic anionic compound RG-13577. RG-13577 mimics the synthetic heparin and specifically binds to the vascular smooth muscle cells (SMCs) and inhibits their proliferative growth. In the molecules of (4-hydroxyphenoxy)acetic acid, the carboxyl groups are held together by R22(8) hydrogen bonds.