When I started reading about SJW, I would read conflicting reports on which type of anti-depressant it is similar to, so I've asked several pharmacists about it, and what they've been telling me is that SJW is odd because it has some of the same characteristics as MAO inhibitors (and, thus, as others have said, you need to follow dietary guidelines as for them), but it also has characteristics like the newer SSRI's (e.g. Prozac) - and thus you need to be careful with other meds that work in a similar manner. (e.g., 5HTP, which has been promoted as a weight-loss drug) You wouldn't want to take both at the same time.
You also need to stay with the same brand & not switch around according to whatever's on sale! Different brands have different actual strengths (look for one that is standardized).
For the last couple of years, the folks who put out the PDR) Physician's Desk Reference have put out an Herbal PDR. If your doc doesn't have a copy in his office, s/he should!
The most recent Herbal PDR says that "recent literature suggests" that SJW does not have MAO effects, but on the next page it lists current use of MAO-inhibitors as a contraindication for SJW's use - so I guess I'd be inclined to be careful & consider it MAO-like until definitely proven otherwise. It also says don't take it with other SSRI's.
Other drugs to avoid while on it -
Other photosensitizers (eg, tetracyclines, sulfas, thiazides, quinolones, piroxicam),
Reserpine, cyclosporine, indinavir, combination-type oral contraceptives, barbiturates, theophylline, digoxin, sertraline, nefazadine.
Also, it has some tannin content, which can inhibit the absorption of iron.
I'm not listing all of this to say that I'm against SJW! I know a lot of people it's worked well for. Just use the precautions.