The Metropolitan Police has begun testing all officers for drug abuse.
Sir Ian said he pledged to tackle "middle class" drug takers
Previously tests were carried out to screen new recruits, but now all ranks including community support officers and specials are liable.
Those suspected of abuse can be tested for drugs including ecstasy, cocaine and cannabis. If positive, the officer must seek help or face dismissal.
A police spokesman said the policy was drawn up with the Police Federation, trade unions and staff associations.
He added that officers who admit abuse would be offered help from an occupational health team and given the support needed to continue in their job.
The new procedure was introduced on 25 January following a change to Home Office regulations in November last year.
The move follows the Metropolitan Police Commissioner's pledge to crack down on "middle-class" drug takers.
When Sir Ian Blair took over control of the force a year ago, he said he wanted to stop cocaine replacing wine at dinner parties.