It’s truly a 21st-century dilemma: Are Tristan and Connie really in love—or is it a side-effect from the new antidepressant that they’re taking as clinical research volunteers? It’s a potent question for the characters in the new Lucy Prebble play, The Effect, directed by Sidonie Garrett (best known for her role as artistic director of the Heart of America Shakespeare Festival) for the Unicorn Theatre through September 30. The cast includes up-and-coming stage performers Manon Halliburton, Todd Lanker, Amy O’Connor, and Rufus Burns. Anyone familiar with antidepressants knows that side-effects, from both veteran drugs and more experimental treatments, can run the gamut—from dry mouth to weeping. Author Prebble’s concern is the sudden passion that arises between two volunteers who are either instantly infatuated or experiencing symptoms of the new drug. Two supervising physicians work at untangling the ethical quandaries as the young couple, Tristan and Connie, risk everything to be together. The Unicorn Theatre production runs September 5 through September 30.