According to the BBC, a survey of almost 200 clinics in England by the National Treatment Agency (NTA), which runs a 500 million-pound-a-year treatment scheme, found users were being offered extra heroin substitute methadone or anti-depressants for clean urine samples.
The NTA admitted the practice was unethical and said it wanted to see certain practices "squeezed out of the system".
The broadcaster reports a third of clinics in the survey said users who produced a drug-free urine sample might be offered increased doses of heroin substitute as a reward - known as "contingency management".
According to The Sun, a quarter admits that clients can choose the type of substitute drugs they want.
The survey also found clinicians offering anti-depressants, cash vouchers or access to detox as a reward.
The NTA said offering drugs for anything other than clinical need was wrong. The agency's chief executive Paul Hayes told the BBC: "It isn't a practice we would advocate.
He said doses of drugs should be determined by an individual's needs and not by whether or not they were co-operating with the programme.