The wildly popular online social networking phenomenon dominated by the Web site MySpace.com has a little-noticed underside: a subculture of users who gather in “groups” - or message boards - expressly focused on dangerous and sometimes illegal activities such as prescription drug abuse, self-mutilation and other types of self-harm.

While most of the hundreds of thousands of groups on MySpace - which claims more than 90 million members, about 20 percent of whom are under age 18 - are built around innocuous interests such as “hobbies & crafts,” “pets & animals” and “romance & relationships,” others cultivate a less savory image.

The Health, Wellness and Fitness category alone contains more than 13,500 groups - some of which offer support, encouragement and advice for those with various illnesses and addictions, while others glorify harmful conditions and behaviors such as anorexia, bulimia and self-mutilation, and advocate the use of steroids for bodybuilding and using prescription pills or street drugs to get high. Group members generally don't know more about the people they're corresponding with than their screen names, reported ages and other generally unverifiable information users choose to include on individual MySpace pages.

Anton Trinidad, medical director of inpatient services at George Washington University Hospital's Department of Psychiatry, expressed alarm about the phenomenon, which has drawn little attention among health experts and about which he said he had been unaware before being asked about it by a reporter.

“It is very disturbing to me that there are many people that are writing on these Web sites that sound to me like they truly have true psychological distress and at the same time they are communicating with people who are giving them advice on how to do harm to themselves,” Trinidad said.

“Mixed with that are tips for where to get (street drugs and illegally sold prescription) drugs. ... (It's) kind of a free-for-all space where impressionable young minds can get the wrong advice or wrong messages.”

MySpace and similar sites, such as Facebook.com, offer a personalized platform for exchanging messages. MySpace users can create personal pages, complete with photos, that express their interests along with such details as sexual preference, relationship status and schools attended. People they identify as “friends” on their pages can leave comments displayed for others to see on the user's page.

To post group messages and exchange private messages on the site, MySpace members first register, free of charge, then create pages describing themselves. This gives them the option to join groups, which serve as an organized collection of messages exchanged between members. Many groups are public - open to any MySpace user; others are private and require approval by a self-appointed moderator before a member can join the group.

Many participants in these groups identify themselves as adults - but some are teens and adolescents who have joined MySpace, in some cases without their parents' knowledge or consent. The Web site says users must be 14 or older but requires no proof of age. While the pages of most MySpace users are “public” and can be viewed by anyone, the profile pages of 14- and 15-year-olds are “private” by default, meaning they can only be viewed by those on their friends list. (Those ages 16 and over now have the option to make their pages private as well.)

MySpace.com, owned by Rupert Murdoch's New-York based News Corp., recently tightened restrictions on users under age 18, preventing adult members from adding a minor as a friend unless they know the minor's e-mail address or full name.

This move came after a Texas girl filed a $30 million lawsuit claiming she had been molested by a 19-year-old man she met on the Web site. (According to news reports, the girl was 13 - though her page said she was 15 - when she met the man on MySpace.)

MySpace executives say they limit access to groups with adult themes to those aged 18 and over. But many groups, including some that discuss drug use, sex and self-harm, can be accessed and read even without a MySpace account.

And many groups with content that parents might find objectionable for their children - including some that encourage drugs, sex parties and “hooking up” with other group members - are not restricted. A 14-year-old user confirmed that he could access many of these adult-themed groups last week.

MySpace executives say the site does protect underaged members. The site asks “members to let us know if the groups they set up are adult,” wrote Hemanshu Nigam, chief security officer of MySpace, in an e-mail interview. “Additionally we monitor the site to identify any groups that may contain adult material and take appropriate action when we encounter them.” MySpace wouldn't say whether the site had warned or shut down any groups. The site also cooperates with law enforcement agencies, said Nigam, and has established a 24-hour law enforcement hot line.

“MySpace members join the community to connect with others around shared interests and experiences, and the groups section of the site is an important component of how the community functions,” Nigam e-mailed. “The MySpace community, like any offline community, permits a wide range of self-expression. ... As a company, we are committed to smart health practices and social responsibility.”

A 14-year-old New Jersey boy - whose MySpace page says he is 19 - belongs to groups including “Pain Pills,” “The Drug Club,” “Pill Poppers” and “i like lying on my bed for hours tripping on benadryl.” He said his parents aren't aware he has a MySpace page or that he goes online to discuss drug use.

In messages exchanged with a reporter through MySpace and filled with misspellings and grammatical errors, he wrote, “My parents have not seen myspace but they do now alot of the things ive done with my life but not to the full extent to which drugs ive take and how many times ... i dont show em, its that simple. in these group we discuss the newest and easiet methods of ingestion ... We talk about legal highs and which pills are good and we also support those who made a change.”

The groups allow users to trade tips and advice or to discuss shared interest in drugs, self-harm or other topics.

On a self-mutilation group called “Razorblade Kisses” - which had nearly 200 members as of last week - a message displays a “Cutting Warning Label” that warns, “before you make that first cut remember. You will enjoy this. You will find the blood and pain release addictive.” And “be prepared to withdraw from others and live in a constant state of shame ... you will find yourself lying to the people you love. You will jerk back from your friends when they touch you as if their hands were dipped in poison.”

Another user responded: “this is so true but its how we live.”

Some exchanges detail where and how to find certain prescription drugs.

In a group called “Pill Poppers United,” a user asked if it's possible to get high off the pain medication Darvocet. One reply suggested hydrocodone instead for a better high.

Another poster in that same group asked about where to find Xanax - which is used to treat anxiety and panic disorder - for a good price, without a prescription. In a group called “Druggies,” a 15-year-old MySpace member started a topic called “Which drug do you like best?” The answers included marijuana, cocaine, ecstasy, OxyContin and crystal meth.

Most of the steroid groups are frequented by bodybuilders. But some also discuss other drugs.

In a group called Steroids & Bodybuilding, for example, a 31-year-old Florida man lists prices for illegal sales of Xanax and Valium, another anti-anxiety drug. “If you have any questions, message me or post em in this thread,” he states, after including the prices for 100, 500 or 1,000 pills of each type.

Robert Roth, coordinator of adolescent behavioral health at Montgomery General Hospital in Olney, Md., said youth who come into his addiction clinic talk frequently of groups on MySpace, and it seems more popular among middle school students than with high school students. The parents of teens frequenting such groups “are usually completely unaware” of what they're doing, he said.

Roth said he warns the adolescents he sees to be wary of any information found online. “Anything you get on the computer, you don't know who's writing it,” he said. But outside addiction programs, many adults appear clueless about the underside of MySpace content.

“I would say that those groups are probably not well known,” wrote the Florida man who posted the drug prices. “I think that most people view MySpace as 'clean fun' and probably don't think much about groups discussing drugs.”