Up to a quarter of students in England are doing degrees that will not give them sufficient earnings to justify the cost of their loans, a think tank says.
The centre-right group urges ministers to cut places on those courses offering little financial return and increase those in post-18 technical education.
Its report also says tax breaks of up to 50p in every pound owed should be offered to graduates repaying loans.
The government is carrying out a review of post-18 education and funding.
The Onward report acknowledges that "education has a value in its own right" and that "earning a living is not the only reason people study" but says too many young people "are being sold a false promise".
"Too many are facing hefty repayments for degrees that won't help them financially and too few are being offered quality technical and apprenticeship options instead," it says.
The study says, in 2015-16:
- between 18% and 25% of undergraduates were studying for degrees that fail to deliver a lifetime-earnings premium that justifies the average student debt, from tuition fees and maintenance loans, of £50,000
- 40% of undergraduates were enrolled in courses that led to median earnings below the student-loan repayment threshold, of £25,000, after five years
- 10% were enrolled in courses with median earnings below £25,000 10 years after graduation - representing 134,000 students every year who won't be paying back anything 10 years after graduating yet who will have accumulated significant interest
- 20% would be no better off five years after graduating than if they had chosen to take a non-university route, such as an apprenticeship
The Onward report urges the government to:
- halve repayments on students loans, by introducing a tax cut for graduates worth 50p in every pound owed
- cut the number of places on courses that offer limited value for money to students 10 years after graduation
- increase the number in post-18 technical education, currently the "ugly duckling" of British education
Co-author of the report and Tory MP Neil O'Brien said: "Too many students are effectively being mis-sold a university education."
There was a "substantial minority who don't earn much but get left with big debts", he said.
"We should steer people away from courses that don't lead to good outcomes."
A spokeswoman for the Department for Education said: "Students rightly expect value for money from their degree, which is why the government is conducting a major review of post-18 education and funding - to ensure we have a system that is joined up, accessible to all and provides value for money for both students and taxpayers."