When two volunteers for an antidepressant clinical trial start to feel the tell-tale signs - sweaty hands, thumbing hearts - they know they have fallen for each other hard. Or are their bodies processing a chemical romance? The question at the heart of The Effect is one for our medicated time, is love the sum of our chemical selves or something more? Four characters, two participants and two supervising doctors with a collective past, are center stage in this investigation of the brain and mood chemistry.