Is an anti histamine which can be used to treat anxiety, in trials it has been shown to be as effective as benaodiazepam with much fewer side effects and hydrox is non-addictive. Hydroxy has interactions with alcohol so you shouldn't drink while taking it (like all anxiety meds). There are questions over hydroxy saftey in pregnancy. Hydroxyzine is usually taken to counter the physical side of anxiety dis-orders.
Im not doctor thats just from wikipedia, active component of Hydroxy Pam is Hydroxyzine, if you wish to read up on it.
St. Johns Wort is a serotonin reuptake inhibitor (amongst other things) taking it is it like taking an extra SSRI and will increase effectiveness of your meds and with that the side effects. Basically dont take ST JOHN's WORT WITHOUT SEEKING MEDICAL ADVICE.
I know St.John's is seen as a natural remedy at that make it appealing to people but it really is potent stuff and carries the same risk as any medical anti-anxiety drug. Bit like taking citaelopram when your already taking xanax.