The amount of time people with severe drug and alcohol addictions can be held for compulsory treatment, is being drastically shortened.

The current law allows for such people to be detained for treatment for up to two years.

MPs have now passed the first reading of a Bill that would allow authorities to sequester people for up to eight weeks, or 16 weeks if the person is brain damaged, so they can be treated for their addiction.

Associate Health Minister Peter Dunne said the proposed change is not a means of social control, it's to provide treatment to those who have no other option.

"The bill is not designed to cure people of their addictions, but it does provide a mechanism by which they can be bought to a point where they can begin to engage in longer-term treatment."

Dunne said it's a long overdue reform of the current law.

"We've moved on from incarceration and isolation as the best way of treating people with substance abuse problems, to understanding that they do better now when they receive their treatment close to their homes and families."