The organised break out happened after dinner on Sunday, said Vu Xuan Thai, director of the detention centre located in the northeastern city of Haiphong.
"Ninety-six of the 201 detainees fled after threatening the guards at the centre with kitchen knives. Police intervened and order was restored," he told AFP.
Some 15 of the escapees have since voluntarily returned and local police are looking for the remaining drug addicts who are still at large, he added.
Vietnam's communist government enforces compulsory treatment programmes for the country's roughly 140,000 drug addicts.
Addicts must undergo two-year spells of compulsory "rehabilitation" in what the government describes as an effort to bring down rising rates of drug use, especially among young people.
US-based Human Rights Watch last year denounced the conditions in Vietnam's rehab centres and a UN expert has recommended they be closed.
The Haiphong rehabilitation centre, which was set up in 1991, takes drug addicts for two-year treatment periods during which time they are expected to learn a trade or perform manual labour, centre director Thai said.
In May 2010, more than 500 drug addicts escaped from another rehab centre in Haiphong.