The party said that, as a first step towards this, it will push for new laws to stop people being jailed over possession for personal use.
Many of the 80,000 Scots left with a criminal record for possession often have mental health issues and this can harm their employment prospects, the Lib Dems said.
Scottish Lib Dem leader Willie Rennie also accused Prime Minister David Cameron of “playing up division” over his attacks on the SNP in recent weeks and the Tories’ “unreasonable” plans to deliver English votes for English laws.
The party’s proposals were unveiled in South Queensferry and also include plans to deliver 20 hours of free childcare for all two- to four-year-olds by 2020 and an extra £800 million for the NHS in Scotland.
The party says it will work with the Scottish Government to see the introduction of a Portuguese-style system whereby those arrested for possession of drugs for personal use are diverted into treatment or civic penalties and do not attract a criminal record.
The party’s business spokeswoman Jo Swinson said: “We need to consider whether or not a criminal record is something which helps people get over an addiction and get on with their lives or whether they may be better off getting the support that they need to get over their addiction.
“Criminalising people when they actually need medical help is not necessarily the best way forward to support that individual.”
Legislation would be introduced at Westminster, which has control over drugs law, to end the use of prison for those arrested for possession of drugs for personal use, under the plans.
Mr Rennie also warned that the prospect of an SNP deal with Labour after the election which hands Ed Miliband the keys to Downing Street would see Nationalists working to break up the UK.
He said: “We don’t think it’s reasonable for the SNP to be in any way in charge of the United Kingdom – that means confidence and supply, that means a formal coalition.
“It’s unfair to put them in charge of an institution that they’re against.
“You can just imagine Alex Salmond as deputy prime minister – as soon as you’ve turned your back, he’s got the screwdriver out trying to take the country apart.”
Mr Rennie also said the Conservatives’ plans for English votes for English laws has been designed solely to benefit the Tories.
“We recognise that the constitution of the UK is evolving but you can’t do a timid reform that doesn’t embrace the necessary wider change,” he said.
“Most devolution that we have implemented in the UK has been a form of proportional representation, but what the Tories are doing are trying to rig it to just benefit them, so that Tories are in charge rather than the people.”
He said the Lib Dems have got a positive programme for Scotland and urged people to back it.
But questioned on whether people should vote tactically to keep the SNP out, he said: “In the 11 seats that we hold, it’s very clear that if you want to stop the SNP, the Liberal Democrats are best-placed to do that.
“People will use their vote intelligently throughout the country and I would encourage them to do so.”