Researchers found that tiny water droplets trapped inside an oil mixture (a water‑in‑oil microemulsion) can carry water‑soluble peptides like GHRP‑6 through the skin, delivering them into the deeper layers without needles. This method worked well in lab studies with insulin, IGF‑1 and GHRP‑6, showing it could be a cheap, stable and painless way to give high doses of proteins, and it even hinted at possible weight‑control benefits. However, it’s still only tested in animals and hasn’t been proven safe or effective in people yet.

A water-in-oil microemulsion is a thermodynamically stable emulsion that has the capacity to 'hide' water-soluble molecules within a continuous oil phase. The very small size of the water droplets within the microemulsion means that these types of formulation can be applied topically to the skin, with the result that peptides and proteins can be delivered effectively into the dermal layer. This review discusses the general problems of peptide and protein delivery following topical application, and compares the possible routes of peptide and protein clearance and distribution within the body following topical administration. Several examples of successful peptide and protein delivery using microemulsions are discussed, in addition to the possible alterations in biological profiles following administration via this route. Water-in-oil microemulsions present themselves as an effective means of topical delivery of peptides and proteins of all sizes, and in high doses. These formulations are a cheap, stable, pain-free means of delivery of peptides and proteins to the skin. An exciting area of potential development is the area of weight control management. The results using insulin, IGF-I and GHRP-6 given topically are particularly intriguing. Whether these results can be replicated in humans and whether the use of these drugs for potential treatment of obesity will be commercially viable will be particularly interesting.