Hexadimethrine bromide (1,5-Dimethyl-1,5-diazaundecamethylene polymethobromide) is a synthetic polymer which agglutinates red blood cells, and used as a heparin antagonist.

Hexadimethrine bromide impedes the proliferation of human mesenchymal stem cells during lentiviral transduction and is deemed non-toxic at low concentrations. Yet, at levels exceeding 10 µg/mL, it adversely impacts the proliferation of certain cell types. Moreover, cells treated with Hexadimethrine bromide and then trypsinized appear significantly enlarged under microscopic examination.