Porous structures made up of Fe3O4 nanoparticles were used to adsorb methyl blue in water. Controlled release of the methyl blue to water was then achieved by application of a magnetic field. Application of a pure DC field did not result in any release. Application of a pure AC field caused released of the methyl blue. However, a combination of both DC and AC fields resulted in much faster release. The mechanism by which this operated is believed to result from viscous friction. Nanoparticles are strongly aligned in the DC field and oscillate under the influence of the AC field. This study demonstrates a concept for controlled drug delivery, where pharmaceutical molecules, similar to methyl blue, would be adsorbed onto nanoporous Fe3O4 structure and the released at a target by application of appropriately localised magnetic fields.