More people will become addicted to hard drugs because of the change in the law on cannabis, according to one of the region's leading drug workers.
Cannabis is now a class C drug
Mandy Stevens, who as resettlement manager works with recovering drug addicts at Yeldall Manor near Maidenhead, believes the move will make drug problems worse.
She said the majority of addicts at the centre start off as cannabis users before moving onto hard drugs.
The drug was reclassified on Thursday, and is now graded as Class C, with steroids and anti-depressants.
"My experience is that it leads onto hard drugs," she said.
She told the BBC that another problem was that many people arrested for cannabis already had hard drugs problems, and they could slip through the net.
"Because so many people won't be arrested, we may lose the opportunity of putting intervention programmes in place," she said.
The government says the law change makes drug laws credible and focuses police efforts on the most dangerous drugs.