This section is from the book "A Practitioner's Handbook Of Materia Medica And Therapeutics", by Thos. S. Blair. Also available from Amazon: A Practitioner's handbook of Materia Medica and Therapeutics.
Hypericum, St. John's Wort. This is purely a homeopathic remedy, and many writers make the ridiculous claim for it that its dilutions will prevent tetanus following punctured wounds. So far as I can determine, the drug possesses astringent and sedative properties especially influencing terminal sensory nerve filaments. In larger doses it influences the nervous system at large.
In large doses (@, 5 to 20 I) it is recommended in nervous and spinal injuries due to shock or concussion, in painful spinal irritation without fever and in suppression of urine due to nervous shock. Probably other agents would serve as well or better in all these indications.
Locally (1 to 2 fK @ to I pint water), it is really a useful remedy in relieving the pain of lacerated and painful wounds in which nerves have been cut or bruised. It very promptly relieves the pain, and can be applied to advantage after proper antisepsis has been first carried out. Upon the unbroken skin it has little effect. The hypericum oil is largely used throughout Europe as an application to recent and painful contusions and excoriations. It appears to give satisfaction when the lesion is superficial. The non-alcoholic hypericum is used by homeopathic surgeons in the treatment of superficial burns. The ones among them who reject the "potency" theory employ this preparation internally in pretty large doses.