A composition comprises: a base oil; an additive; and a drug. The additive has segments which are conjugated, e.g. covalently linked, together. A first segment facilitates solubility in the base oil, whereas a second segment facilitates drug solubility and/or modifies drug release or other behaviour. The first segment may for example comprise a poly(dimethylsiloxane)-containing moiety. The second segment may for example resemble a drug molecule. The composition may for example be used as a tamponade or as a component for a tamponade administered to the eye.