Lindsay LohanThe reason you haven't seen many tweets from Lindsay Lohan is because she's not allowed on Twitter in rehab.

According to a source, the actress, who is getting treatment for substance abuse problems at the Betty Ford Center, is "only allowed to use her phone for two hours a day, and only to keep in touch with family and close friends," The New York Post reports.

"Before, she would repeatedly and compulsively e-mail her friends if she was ever in a situation where she felt lonely, and she would vent on Twitter," the source continued.

The phone policy is standard for all Betty Ford patients, so the troubled starlet can "concentrate on herself," the insider explained.