This invention relates to novel structural analogues and derivatives of compounds with general analgesic or related pharmacological activity. In particular the invention relates to derivatives of opioid compounds, particularly morphine and related compounds, in which an opioid compound is linked via the nitrogen at position 17 to a spacer group, which in turn is linked to a charged group, or a pharmaceutically acceptable salt thereof. In particularly preferred embodiments the opioid compound is morphine, codeine, or buprenorphine.