One Bay individual with a substance addiction has been receiving the invalids benefit for 25 years.
Under welfare reforms passed in July, sickness and invalids benefits were repackaged to become Jobseeker Support and Supported Living Payment.
Beneficiaries on Jobseeker Support can be exempt from work obligations if they have a significant injury or health condition, but must seek at least 15 hours' work each week if their health practitioner determines they are capable.
Miss Hamilton said she was surprised the number of drug-addicted beneficiaries had dropped.
Over the past four to five years, she had noticed an increase in the number of people using synthetic cannabis, which was difficult to screen in workplace drug tests.
More young people in particular were using synthetic highs. "Because it's legal they want to give it a try," she said.
However, it caused substantial damage to users, including depression.
She knew of long-time marijuana users who had switched to synthetics to avoid positive drug tests.
"A lot of people are shocked at how unwell they become so quickly and how hooked they become on it.
"We're all surprised in the industry how the synthetics can cause so much damage in such a short time."
Alcohol was still the most prominent and socially acceptable drug being abused, she said.
"From my work, it's one that causes the most problems."
There were a minority of beneficiaries suffering traumatic brain injuries from long-term substance abuse who would probably never work again, she said.
"But what I know is the more addicts can become clean and sober, the more they participate in society and live life, and the more likely they are to stay clean and sober."
Beneficiary Advocacy Federation spokeswoman Kay Brereton said substance abuse covered a broad range of problems, from those addicted to painkillers prescribed for a medical condition, to those with an illegal drug habit. Long-term addicts were often using substances to cope with past trauma and could not become work-ready in a set time frame.
However, "semi-medical" staff at the Ministry of Social Development (MSD) had begun second guessing doctors' assessments and asking them to change their medical opinion in order to get beneficiaries back into work, she said.
While there was nothing wrong with MSD seeking more clarity on doctor assessments, it had to be transparent.
Work and Income associate deputy chief executive Liz Jones disputed the claims.
"Clients need a medical certificate from a GP if they are unable to work because of a health condition or disability, so we are certainly not discouraging doctors from writing medical certificates," she said.
