Melissa Reid, 20, of Lenzie, East Dunbartonshire, and Michaella McCollum, from Northern Ireland, were transferred from a prison in the capital by van wearing handcuffs to face the charges.
The pair both entered pleas admitting they attempted to smuggle 11kg of cocaine with an estimated £1.5m street value onto a flight bound from Lima for Spain in August.
The pair had originally claimed they were coerced into taking the drugs on behalf of criminal gangs who also threatened their families.
Reid and McCollum's U-turn avoids the need for them to be tried on drug trafficking charges, which would have carried a heavier sentence had they been found guilty.
Instead, it is likely they will be sentenced to six years and eight months in jail at a hearing likely to take place next week.
A court spokesman confirmed the pleas, adding: "Both women have pleaded guilty to drugs trafficking."
"It means they automatically benefit from a sixth off the minimum jail sentence of eight years and will be sentenced to six years and eight months in prison.
"Sentencing has not taken place yet and a new hearing where the women will be sentenced has now got to be arranged.
"But it's likely that will take place in around a week's time."
Reid and McCollum had previously been working in Ibiza and travelled to Peru to commit the crime from there.
They had been facing up to 15 years in prison if they had been found guilty in a trial.
Their lawyer at the court would not comment.