Souvara appears as a grey powder with pearly granules. Chemical analysis simply shows the presence of an alkaloid unknown to Western science. It is very rare and can only be found in Asia.
Besides being an addictive narcotic souvara causes the user to experience past lives. After several usages the effect will occur even without the use of the drug.
The drug is taken dissolved in a glass of pure water. At first visual perception is increased. Then objects seem to extend unexpectedly. After this they begin to become transparent. Once these have vanished a series of scenes will flash by showing the users past lives.
If a past life contains a profound shock, especially contact with the mythos, the user will re-live that life completely, not noticing their future life until the scene is over. This effect will happen again during subsequent usages of the drug, and can occur even after usage has stopped.
One such user is the novelist John Milwarp. Taking the drug he discovered one of his ancient lives, a priest living on the planet Hestan, sinned against the time god Aforgomon. This caused the god to curse the priest, and all his future lives, to die horribly, and to dissolve from time once John Milwrap experienced the priest's sin and punishment.