Lofexidine exists as a solid at room temperature, with a melting point of 127 degrees C. The pair of ortho chlorine (Cl−) atoms on the phenyl ring are necessary for lofexidine's agonism at the α2a adrenergic receptor subtype; removal of either chlorine atom results in antagonism at the receptor. Lofexidine is structurally analogous to clonidine, another α2 adrenergic receptor agonist used for treatment of opioid withdrawal symptoms. A comparison of the two structures is shown at right. Both contain an imidazoline ring and a 2,6-dichlorinated phenyl ring. The differences in structure are shown in red, while the similarities are in black. In addition to the structural differences, administration of lofexidine to people who abuse opioids has been shown to be more effective for a longer duration, with fewer withdrawal symptoms than clonidine even after one day. However, clonidine is often preferred as it is substantially cheaper than lofexidine when purchased with a private (non-NHS) prescription. This factor is exacerbated by the considerable number of and quantities of medications prescribed to alleviate the constellation of withdrawal signs and symptoms. Additionally, clonidine has been shown to significantly lower blood pressure. Therefore, although similar to lofexidine, clonidine is most frequently prescribed to treat high blood pressure. Britannia Pharmaceuticals has licensed lofexidine to be sold by US WorldMeds for sale in North America. In the United Kingdom, the hydrochloride form, lofexidine HCl, has been licensed and sold since 1992 for opioid withdrawal relief in tablet form as BritLofex by Britannia Pharmaceuticals. BritLofex is only available by prescription. Lofexidine was first approved by the US FDA on May 16, 2018 under the brand name Lucemyra, produced by US WorldMeds. It was noted as the first, non-opioid drug approved in the US for the treatment of opioid withdrawal.