Young people caught with small amounts of drugs should not have their job prospects destroyed by "ludicrous" laws, Nick Clegg will argue.
The deputy prime minister will explain that a 19-year-old cautioned for drugs possession for personal use has to declare the offense for six years when job hunting.
"In this country, if you're a young person – say out at a club with friends – and you get arrested for possession of a small amount of drugs, it's likely you'll end up with a criminal record," Clegg will say.
"That means this stupid, youthful mistake could damage your whole future – possibly stopping you from getting the job you want, whether it's as a doctor, nurse, teacher or even as a taxi-driver.
He will add: "I just don't think it is right for us as a society to write off these young people who haven't hurt anyone else, just made the wrong choice, so early. We need to put an end to this ludicrous situation.
"Our focus should be on getting them the help they need, not punishment, so they can go on to realise their ambitions and make a positive contribution to society."
Clegg will also announce that a Liberal Democrat government would move drug policy from the Home Office to the Department of Health.
Clegg is expected make the speech alongside drug law reform proponent Virgin founder Sir Richard Branson.
The manifesto commitment will come with 63 days to go before general election in May.
The latest opinion poll from YouGov for The Sun had the Liberal Democrats on just 5%, well below the party's 2010 result of 23%.
The survey, which questioned more than 1,700 voters between 2 and 3 March, also had the Tories on 36%, Labour on 34%, Ukip on 14% and the Greens on 6%.