St. John's wort (Hypericum perforatum) is an effective and relatively side effect free anti-depressant for some forms of light-to-moderate depressive disorders. It does interact adversely both with synthetic anti-depressants and with other drugs, so self-medication with St. John's wort is even less advisable than it is with other herbal remedies.
Applied externally, an oil extract of St. John's wort flowers and leaves can soothe burns and support wound healing. There is also some evidence of the oil extract relieving muscle pains and inflamed joints.
In fiction, St. John's wort placed on window sills and over doors keeps unfriendly Fae at bay and other monsters at bay.
St. John's Wort in Modern Herbal Medicine:
St. John's Wort in Fiction:
In modern medicine, St. John's wort is used increasingly often as a treatment for mild-to-moderate depression since it has fewer side effects than traditional anti-depressants. If there's a little weasely voice inside your brain, constantly telling you you're worthless - taking St. John's wort as an anti-depressant may help you fight off that only-too-real monster. (*)
In fantasy stories, the herb wards off more tangible (if fictional) monsters. Take for example this snippet from Fire Touched by Patricia Briggs, where the main character Mercy Thompson is attacked by a troll:
It was probably coincidence that I remembered the essential oil that Zack had shoved into my pocket as soon as I touched the walking stick. I pulled it out of my pocket and saw at a glance that Zack had gotten it right, grabbed the Rest Well and not any of the other oils that I'd bought. The Rest Well had been mostly St. John's wort. [..]
For lack of any better idea, or any more time to fuss, I swept my hand out from left to right, scattering the liquid in front of me in a rough semicircle. [..]
I narrowed my eyes at the troll and thought, Bring it. The troll, so close that I could feel his breath, stepped on the pavement where I'd dropped the essential oils and staggered back as if he'd hit a wall.
There are quite a few sources confirming the effectiveness of St. John's wort against fairies (or the Fae, as they're called in Brigg's Mercy Thompson series), as well as several others that claim the herb as a defense against other magical creatures, or the blights and illnesses they may cause.
Usually, though, the herb itself is used, either by ingesting it or by putting a living or dried plant onto window sills or hanging it over a door. Mercy in the above snippet is lucky: The herb's magical properties have apparently survived the distillation process that created the essential oil she's using against her otherworldly attacker.
*** Please note: This blog is not intended as medical advice. ***
Do not try this at home.
(Or at least, don't use any of the remedies described here this without consulting your physician first.)