Transdermal drug delivery involves application of drug(s) to the skin for systemic effects. However, relatively few drugs possess the necessary properties to passively traverse the skin’s stratum corneum barrier. Microneedle (MN) technology is a novel drug delivery technology that increases skin permeability by creating microscopic pores within the skin through which the drug can diffuse passively to the dermal microcirculation. This overcomes the barrier to efficient drug permeation. This thesis focuses on the potential of hydrogel-forming MNs to deliver the hydrophilic and high dose drug, metformin HCl, transdermally. Hydrogel-forming MNs were evaluated and showed extensive swelling capacity in PBS (pH 7.4), sufficient mechanical strength and penetrated the validated skin model, Parafilm® M, consistently. Metformin HCl was formulated in lyophilised drug reservoirs and combined with hydrogel-forming MNs to form an integrated patch. This patch was tested in vitro and in vivo with metformin HCl permeation determined. This work is the first report of hydrogel-forming MNs used for the enhanced delivery of metformin HCl. Fundamental evidence is presented that confirms the ability of hydrogel-forming MNs to deliver hydrophilic compounds, like metformin HCl transdermally. This could offer considerable patient benefit, as the number of drugs available in a transdermal form could be vastly increased. Looking towards translation to practice, this work provides evidence of a suitable formulation strategy for water soluble drugs to be delivered using hydrogel-forming MNs.