DEA special agents and California Medical Board investigators posed as patients seeking prescriptions for controlled substances during six undercover visits.
Investigators say on five of those occasions, Tseng issued prescriptions for Vicodin, Suboxone and Xanax without taking medical histories and either not conducting a medical examinations, or just a cursory one.
The DEA says the prescriptions were often made for no legitimate purpose.
There are also reports that the doctor's prescriptions may be linked to eight overdoses.
Tseng denied any wrongdoing and said "I really believe I did nothing wrong."
Doctor Tseng's suspension is temporary.
An administrative hearing will be held to determine if the suspension will become permanent.
City News Service contributed to this report.