A former Massachusetts chemist accused of faking test results at a state drug lab has pleaded not guilty to four counts of obstruction of justice in a scandal that could jeopardize thousands of drug convictions.

Annie Dookhan was indicted on a total of 27 charges accusing her of fabricating test results and tampering with drug evidence while testing substances in criminal cases.

The 35-year-old Dookhan was arraigned Wednesday on four obstruction counts in Brockton Superior Court. She was scheduled to be arraigned later Wednesday on additional charges in Fall River Superior Court.

An estimated 200 convicted defendants have been released from jail and had their cases put on hold while their legal challenges are pending.

Authorities shut down the lab in August.