Banshara

The i (singular Banshara) were a species that, according to the First Doctor, had a chemical dependence on endorphins, specifically love.

During World War II, three Bansharai that had crashed on Earth appeared to Barbara Wright, Julia Miller and Sarah Miller as someone they loved. However, Barbara and Julia rejected their Bansharai; the Bansharai weakened until Sarah's Banshara found them and, reunited, the three were able to regain their health. This allowed them to leave Earth. (PROSE: Tell Me You Love Me)