The figures, published in an annual report from the Scottish Prison Service (SPS), are further confirmation of the scale of drug-taking in the prison estate north of the Border.
The SPS will present its findings at today’s Holyrood health committee, which is taking evidence on the Scottish Government’s drug strategy.
SPS bosses added that a survey ound 39 per cent of prisoners reported seeing illegal drug use in prison in 2017.
The same Addiction Prevalence Testing (APT), which is conducted across all Scottish prisons annually, stated that 76 per cent of inmates analysed tested positive for drugs on admission to jail.
Tory MSP Liam Kerr said the findings would alarm the public, who expect prisons to be secure environments, and harm the prospects of rehabilitation and reducing reoffending.
But the SPS said the upsurge was due to an increase in funding aimed at tackling the problem.
Mr Kerr said: “Prisons are supposed to be absolutely secure environments, where nothing gets in or out that isn’t supposed to,” he said.
“So for drug use to be so rife in Scotland’s jails is alarming.
“People understand there will always be examples where smuggled items can slip through the net.
“But for one in three inmates to be testing positive on release is an incredible statistic.
“It raises real questions about how serious the SNP government is when it comes to keeping drugs out of jail.
“There is no hope of rehabilitating prisoners while illegal substances are circulating with such ease.”
A spokesman for SPS said: “We take the business of people bringing drugs into prison extremely seriously. We have invested heavily in intelligence gathering and technology to combat the menace of drugs.
“It should come as no surprise that we are seeing more inmate caught taking drugs as result.”