Controversial benefit changes could lead to more drugs deaths, make war veterans homeless and put children at risk by placing them in a shared home with strangers, according to housing organisations.
Benefits claimants will soon see their money paid into their bank account in a single "direct payment", rather than channelled straight to landlords and other support agencies.
They will then be expected to manage their money accordingly, but housing bodies have raised fears that drug addicts and alcoholics may use it to fuel their addictions rather than pay their rent and bills.
The UK Department of Work and Pensions' controversial welfare reforms will also encourage housing bodies to tackle "under-occupancy", to cut down on the number of single people living in properties with two or more bedrooms. But one housing body raised concerns that this could lead to more pressure to house unrelated tenants together or force currently single tenants to take a lodger, with knock-on effects for child safety.
The fear that vulnerable tenants may spend their direct payments on drugs and alcohol was a major concern for two housing bodies at Holyrood's Welfare Reform Committee.
Ken Milroy, chief executive of housing charity Aberdeen Foyer, said: "We have seen people with addiction issues when they come out of prison with a low tolerance, and we see drug deaths. If the money goes to an individual, rather than the landlord, and they are in a vulnerable situation, we could potentially see an increase in overdoses."
He added: "We have asked those that we work with what they would have done with the money, would they have paid their rent or would they have bought drugs with it? The answer has been, 'We would have bought drugs'.
"So, I don't know why we want to put people who are clearly vulnerable in a more difficult situation by the mechanism of direct payments. It's a fear that we have and I think it's grounded by the experience that we have got by working with our client group."
Ian Ballantyne, chief executive of the Scottish Veterans Housing Association which specialises in housing armed forces veterans, said: "You could give a gross alcoholic, of which we have quite a few, a huge amount of money, provided of course they can get a bank account to pay into. I would support what Ken (Milroy) says. What do I do? Do I say, 'I must pay my rent', or do I go to the pub across the road?"
A Department for Work and Pensions spokeswoman said: "We are carefully working with councils and housing associations in Scotland as our welfare reforms are being introduced to ensure vulnerable people are protected. Alarmist claims about the effects of welfare reform are simply scaremongering."