It really depends on what you mean by drug free. If you mean not treating with the hard synthesized chemicals like Apistan and checkmite, than good success can be had with organic acids such as formic and oxalic. If you mean no treatment at all, nada, none, than your best best is to start with local survivor feral stock. I have migrated all my stock from local survivor stock and am going into my 4th year of no treatment. I have some on small cell and some on large cell and they seem to do equally well.