Is there a difference between ‘us’ and our brain chemistry? Though (given the rise of AI) it’s not the most zeitgeisty of questions about human consciousness, Lucy Prebble’s The Effect certainly gives us good cause to think it over anew. We are thrust into a medical trial – the Burton Taylor Studio arranged in traverse, with two banks of seating either side of the performance space, so that we, too, know ourselves to be observers, observed. Connie Hall (Rose Martin) and Tristan Frey (Alec Day Greene) are helping test a new antidepressant – but is it also responsible for the growing chemistry between them?

Martin and Greene bring that relationship to life with extraordinary flair. Greene plays the carefree wannabe traveller with ease, self-aware but not self-conscious in his languid physicality. Connie’s character, meanwhile, is grounded in an anxiety which Martin vividly conveys in performance. Even though their initial conversations overemphasise these oppositions a little – and Tristan’s immediate boyfriend-related questions sit a little uneasily – there is genuine humour in seeing the two relax into being with each other. Part of that process is discussing the meaning of the trial itself for their relationship: Connie, a psychology student, puts forward the materialist perspective that we are determined by our physical state and nothing more; Tristan’s religion expresses itself in his continued gestures towards something more transcendental. The constant anxiety is whether or not what they are feeling is ‘real’, and whether that matters.

They are watched over in this process by Dr Lorna James (Robyn Hayward), at first little more than a supervisor administering psychological tests and noting Connie and Tristan’s self-reported symptoms. In her behind-the-scenes conversations with the drug’s developer, Dr Toby Sealey (Rohan Joshi), however, Dr James begins to reveal her real character. Hayward’s switch between these two modes is magnificent, expressing private doubts which completely change how we see her interactions with the patients. A structural symmetry between the two pairs quickly becomes evident; James and Sealey’s relationship is more uncertain, however. They begin with spiky discussions about the drug’s efficacy, before moving into the even thornier terrain of whether medicating mental health conditions is itself an appropriate response. Joshi plays Sealey very much in the mould of the earnest Silicon Valley entrepreneur, every inch the polished public speaker when he gives the audience his TED talk that ‘all health is physical health’. His sincerity is genuine, even if we, with James, might question his beliefs. The dialogue brings weighty contributions to every side of the debate around mental health medication; the actors ensure those contributions are made with deep humanity.

The Effect is not simply a staged debate, however. Connie and Tristan, hijacked by the drug and the pressure of the trial, become evermore agitated, bursting across the stage as they shout their symptoms to Dr James. This is the moment in which the traverse seating arrangement shines most, as  the play makes something of being able to play to two audiences. Each extra dose of the medication is another moment of pressure, the thrumming bass loops in the background suddenly ramping up as red light spills across the stage. It’s a club atmosphere – another space where social norms dissolve and relationships accelerate, with a little help from drugs legal and experimental. The flickering lights and bass stings persist even in some of the more realistic moments. Paired with the evocative soundscape the audience walks into (my notes are ‘funky bubble spooky noises’), they key us in to the fact that things can go very wrong very quickly even in as controlled an environment as a medical trial.

The second half of the play becomes more personal, moving away from the logistical and ethical intricacies of a medical trial to become firmly rooted in the relationships between these two pairs of characters. The routes they take to get there are circuitous enough that I can’t discuss it in detail; but in itself it is evident enough that, no matter what the circumstances, relationships will always be complicated, emotional, perhaps illogical, and, in that, deeply human. That much, The Effect tells us, no drug will be able to change.

[The Effect, staged by Fennec Fox Productions, is running at the Burton Taylor Studio, 2nd-6th June, 2026].