Since Lucy Prebble’s play “The Effect” premiered in London in 2012, theater directors around the world have had creative license to interpret the drama in their own ways onstage. Connie and Tristan are testing a new drug that stimulates the feel-good dopamine receptors in the brain. But is this relationship an effect of the drug or is it simply human nature taking its course? A new production of “The Effect” opened Friday at OnStage Playhouse in Chula Vista. Through Oct. 12 (plus 7:30 p.m. Sept. 29)Where: OnStage Playhouse, 291 Third Ave., Chula VistaTickets: $15-$25Online: onstageplayhouse.org