Multiple prisoners were taken to hospital on Christmas Day amid widespread drug misuse at a Clackmannanshire prison.
A total of 35 inmates at HMP Glenochil were found to be under the influence of drugs on 25 December, with five transported to hospital for treatment.
It is thought the drugs may have been delivered to the prison via drones.
It is understood the affected prisoners have since recovered.
Drugs, weapons and mobile phones were seized by prison staff during the incident.
A Scottish Prison Service (SPS) spokesperson said: “Any attempt to bring illicit substances into our establishment, including by a drone, poses a significant threat to the health and wellbeing of those in our care, and the safety of our staff, and we will use all technological and intelligence tools available to prevent this wherever possible.
“We continue to work with Police Scotland, and other partners, to take action against those who attempt to breach our security.”
Police Scotland was contacted for comment.
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The number of drones caught flying into Scotland’s prison estate increased a few years ago amid a crackdown on prison letters.
A policy change allowed staff to photocopy letters addressed to prisoners, so inmates receive copies rather than originals.
The measure was put in place to stop drugs – in particular, benzodiazepines like etizolam – from entering the estate as smugglers had been using the mail to soak drugs into the paper.
At the Scottish parliament last summer, Justice Secretary Angela Constance said: “Both the Scottish Prison Service and Scottish government are fully aware of the negative impact of drones being used to introduce illicit items into our prison estate and understand the threat that this has on operational stability of our prisons.
“A technological response to support the identification of drones within SPS airspace is currently being piloted.
“This should provide vital evidence to support wider use of this technology throughout the rest of the prison estate.
“The health and wellbeing of those who live and work in prison remains a priority for this government.”
