African Dream Root

African Dream Root (Silene undulata or Silene capensis) is also known as Ubulawu or Xhosa. The plant has been used in southern African in spiritual rituals for centuries. It contains a psychoactive compound (not yet identified) that produces intense and imaginative dreams.

There are several methods to prepare it:

Either half a teaspoon is mixed with half a cup of water and drunk on an empty stomach, or a heaped tablespoon is mixed with half a liter of water, and the water is blended until a froth is formed. The froth is drunk before going to bed. The tea made out of African Dream Root has an ocher color. ^Source

Traditionally, African Dream Root is used to communicate with one's ancestors.

In 3.10 Dream a Little Dream of Me, it is prescribed to Jeremy, a man who hasn't dreamed in years. Jeremy misuses the power of the root to enter other people's dreams and control them (Dreamwalking). To achieve this, he adds some DNA of the person he wants to visit in his dreams to the tea.

It is also used by Dean in 8.20 Pac-Man Fever to enter Charlie's Djinn induced nightmare, which is killing her.

DREAM TEA RECIPE
3/4 inch piece of African dream root
1 tablespoon ground ginger
1 tablespoon cinnamon
1 teaspoon honey (or sugar)
1 uncontaminated piece of dreamer's DNA (hair, saliva , boogers, eyelashes, skin...)

Grind root with mortar and pestle, mix in ginger and cinnamon. Place ingredients in a mug and stir in one cup boiling water. Add in honey, stir, then let steep for two minutes. Add milk or cream to taste.
Drop in DNA.
It's recommended you enjoy this beverage in bed as you will fall asleep within seconds of finishing. Then it's off to Never Never Land. Sweet dreams.

Source: Supernatural: The Official Companion Season 3