Hundreds of thousands of people who look after loved ones north of the Border face financial strife, and many are accumulating unmanageable debt.
The 12-month investigation by Carers Scotland and Carers UK found that 59% of carers are "fuel poor", while almost half are in debt as a result of their responsibilites.
The Caring and Family Finances Inquiry claims 170,112 of Scotland's 660,000 carers have given up work to care at some point, but now many are struggling with loss of income and savings and cuts to benefits at the same time as the cost of living is rising.
The charities surveyed more than 5000 people across the UK who look after someone who is older, disabled, or seriously ill. They also held focus groups.
The resulting report claims that while there has been a rapid rise in the number of families providing care to loved ones in recent years, support to carers has faced cuts from the UK Government which it is estimated will reach a cumulative £1 billion by 2018.
Simon Hodgson, director of Carers Scotland, said it made sense to provide more help. "Those caring, unpaid, for loved ones save society vast sums, but at huge personal cost - a cost this inquiry shows is pushing families to the brink," he said.
Caring is often a dual blow, with household incomes hit by reduced earnings and bills rising as a result of the extra costs of ill health or disability."
Pressures include the so-called bedroom tax, which has so far affected 60,000 carers, although the Scottish Government has pledged to change this north of the Border, and the scrapping of council tax benefit, which has left 240,000 carers having to pay council tax in full. A total of 24,000 fewer carers are getting carers' allowance due to the knock-on effects of tougher rules and tests for disability benefit claimants.
The report also draws attention to the size of the Carers' Allowance - £59.75 a week for those caring for a minimum 35 hours, the equivalent of £1.67 an hour, dropping 35p an hour for anyone providing 24-hour care. Even this sum is withdrawn if a carer earns £100 a week, the authors point out.
The report says the current situation is becoming unsustainable for many families, and points out that carers save government and social services money. "The costs to the exchequer, local authorities and the NHS of having to replace family care are extremely high."
Carers can incur higher expenses, due to the need to keep heating on for longer if people in the family home are sick, bigger laundry costs for those with incontinence or feeding tubes, and higher food bills for those nursing someone with a special diet, the report argues.
"With an ageing population more of us will care for loved ones - yet a blizzard of cuts to social care and benefits means there is less and less support available. This is unacceptable and unsustainable," Mr Hodgson said.
Carers Scotland is calling for the UK Government to urgently reform the financial help on offer to carers and review the impact of benefit cuts on carers. Meanwhile both the UK and Scottish Governments should introduce a test to ensure all benefit and social care changes do not leave carers worse off, it says.
Jackie Baillie MSP, Labour's spokeswoman for social justice and welfare, said: "There are hundreds of thousands of carers in Scotland who among other things make a massive contribution to the economy.
"It is therefore unfortunate to say the least that the direction of government policy is such that carers are finding themselves plunged into poverty as a result of caring."
A Scottish Government spokesman said: "Being a full-time carer for a loved one can be a difficult and isolating experience at times and we must ensure that carers receive the support they deserve.
"Despite Westminster's programme of welfare cuts, we are doing all we can, with our limited powers, to alleviate the burden of poverty. This includes providing an additional £9.2 million to the Scottish Welfare Fund. In addition, we have committed over £112m to support carers and young carers between 2007 and 2015.
"However, only an independent Scotland would have full control of the welfare system in order to protect our most vulnerable."
A Department for Work and Pensions spokesman said: "We recognise that carers provide an invaluable service to people in some of the most vulnerable circumstances in our communities. That's why we're spending around £2bn this year on Carers' Allowance, and even more in the future."