i want to be friends with katherine...

The Ativan came from a former colleague who had traded it to her for the Vicodin that Katherine's boyfriend had been prescribed by a dentist. The boyfriend did not mind, but he preferred that she not give away the Ambien she got from a doctor by exaggerating her sleeping problems. It helps him relax after a stressful day.

"I acquire quite a few medications and then dispense them to my friends as needed. I usually know what I'm talking about," said Katherine, who lives in Manhattan and who, like many other people interviewed for this article, did not want her last name used because of concerns that her behavior could get her in trouble with her employer, law enforcement authorities or at least her parents.

For a sizable group of people in their 20's and 30's, deciding on their own what drugs to take - in particular, stimulants, antidepressants and other psychiatric medications - is becoming the norm. Confident of their abilities and often skeptical of psychiatrists' expertise, they choose to rely on their own research and each other's experience in treating problems like depression, fatigue, anxiety or a lack of concentration. A medical degree, in their view, is useful, but not essential, and certainly not sufficient.

They trade unused prescription drugs, get medications without prescriptions from the Internet and, in some cases, lie to doctors to obtain medications that in their judgment they need.