I've had GAD and recurring depressive episodes for over 10 years. I've taken St. John's Wort (Kira/Jarsin brand) at 900mg/day since 2009. It worked quite well at first but in recent years I got high anxiety and depressive episodes even on my regular dose. I'm now seeing a psychiatrist who has a lot of experience working with both prescription antidepressants and supplements and he is transitioning me from SJW to escitalopram over the course of a few weeks. He realizes that serotonin syndrome is a theoretical possibility but by dropping the SJW to 600mg first and only starting at 5mg escitalopram (and reducing SJW further before going up to 10mg), it should minimize the chance.
For background, I've taken amitriptyline and 5-HTP (at separate times) with SJW in the past and not had any ill effects.
Since this is probably a fairly unusual transition, I'm posting my experience here to let everyone know how it goes. I dropped to 600mg SJW 3 days ago and will be taking my first 5mg escitalopram dose tomorrow morning; I'll post more updates as anything of interest occurs.