BERKELEY (CBS SF) — Three armed, masked robbers robbed a medical marijuana dispensary in Berkeley early Sunday.

The robbers tied up the security guard posted outside the Berkeley Patients Group and made off with three trays of marijuana plants, according to police.

It happened around 1:20 a.m. in the 2300 block of San Pablo Avenue.

BPG is one of the nation’s oldest and biggest medical marijuana dispensaries. Spokesperson Victor Pinho told Berkeleyside it was the first time in the 16 years the dispensary has been in business that a robbery occurred.

He said the security guard was not harmed and the robbery was caught on surveillance video.

“A full investigation is underway by the Berkeley Police Department,” he said. “Our security measures were in fact successful.”