A common weed here in Southern California, this plant is far more deadly than the Deadly Nightshade. It's mind altering powers are so awesome even people heavily into "recreational substances" have generally shunned it. All parts of the plant are highly toxic.
Unlike psilocybin or LSD, which cause sensory distortion, datura is a true hallucinogen, transporting the user entirely into another reality with little or nothing of this reality to hang on to. An additional problem is that there is little margin between the effective dose and a fatal dose. Persons who have heard of this plant but not studied its use thoroughly often take a dose and find no effect - so they take a second dose of similar size and die.
The expert advice is "Don't", but if you do be very, very careful and have adequate and adequately briefed support staff on hand with access to emergency care. Keep in mind that if the user's personality is not rock solid (does not describe most recreational substance users) it's likely to become completely unglued.
More on Nightshades.