An number of potential drugs, including steroidal drugs are extremely water insoluble, limiting their commercialisation as medicines. Solubilisation of drug in surfactant micelles is a means of increasing the apparent aqueous solubility of a drug and ensuring exploitation as a medicine. Micelles formed by the anionic surfactant, sodium dodecyl sulphate, have been shown to be an excellent solubiliser of steroidal drug. Changing the counterion has been shown to influence solubilisation in a micelle with lithium increasing solubilisation and ammonium decreasing solubilisation. We aim to determine the effect of the counterion ion on the stiochiommetry and the nature of incorporation of steroidal drug into monolayers formed by different dodecyl sulphate surfactants, namely those containing either Li or NH4 counterion, using neutron reflectivity in combination with contrast variation.