It was used as an infusion for coughs and colds, or made into an ointment to be put on bruises, scratches or insect bites.
The plant has been historically associated with John the Baptist, hence it's common name. John the Baptist's birthday was at the summer solstice, an important day even in pre-Christian times, and some think that the bright yellow flowers were associated with that day. In addition to the medicinal uses, plants of this herb were hung over doorways and used in exorcisms.
Since I've started on Hypericums, I might as well show you some of the others that we grow.
Hypericum 'Blue Velvet is a small shrub with blue green leaves and the bright yellow flowers that are typical of the Hypericums. Ours grows in light shade where it gets a half day of sun and seems quite happy.
This one is 'Hidcoat Variegated', about which I know nothing, I hate to admit. Hank bought it (I think he'd buy anything as long as it was variegated) and it seems happy here so far.
And last, this is 'Tricolor', though in sun, there are surely more that 3 colors, the pink, white and several shades of green. This, I think, is a zone 7 plant, but because we like it so much, we go to great pains to keep several of them alive. Without a wrap or cover of burlap over the winter, they wouldn't make it until spring. It has been very slow growing and took many years to finally flower. Still, it seems worth the extra fussing we need to do for it in the fall to prepare it for winter. We've had it in the gardens for at least 15 years, so we must be doing something right.