The Irish Prison Service (IPS) is managing 200 prisoners who are "closely aligned" to 14 criminal groupings, but the figure does not include dissident republicans held in high-security Portlaoise Prison.
In an interview with the Herald, IPS director-general Caron McCaffrey said the 1,425 seizures this year up until late November were due to a number of factors.
She said drug use in prisons remains a "significant issue", with 70pc of inmates coming into prison with addiction problems.
Covid-19 protocols such as the mandatory quarantining of new inmates for 10 days have thwarted many prisoners who would traditionally have hidden drugs in their bodies for distribution in the jail system.
Drugs being thrown into prisons in metal pipes so the contraband can pass through protective overhead netting in the facilities remains a significant problem.
Operation Throwover, targeting such incidents at Wheatfield and Cloverhill prisons, led to 81 incidents being detected and 19 prosecutions up until the end of September.
Prison staff have recorded an increase in attempts to smuggle drugs using impregnated paper in letters sent to inmates through the postal system.
Staff have used modified ion scanners to detect letters that have been pre-soaked in drugs such as spice and acid.
Ms McCaffrey said she recently met with senior gardaí to discuss the growth of organised criminal gangs and the increase in drugs in the prison system.
The biggest drug seizure of 2021 in Irish prisons happened in October when around €140,000 worth of drugs and 15 mobile phones were recovered in Mountjoy Prison, hidden beside a sink. Ms McCaffrey said such activity is linked to "serious organised criminality".
That seizure, along with another in the same prison last year, came about as a "result of intelligence that we received on our confidential telephone line".
Ms McCaffrey said she encourages people to use this phone line in an attempt to curb the supply of drugs in jail.
Up to late November, 1,290 illegal mobile phones were seized, along with 279 weapons.
Drones were an increasingly common way for drugs to be smuggled into prisons, but the IPS is satisfied that the anti-drone tech technology it has deployed in six prisons across the country has greatly counteracted it.
In October, there was concern when high-profile gangland criminal John Mangan absconded from Loughan House open prison in Co Cavan. He was one of a number of prisoners to simply walk out of the two open prison facilities in Ireland. He was caught several weeks later and returned to a stricter prison regime.
Ms McCaffrey defended the IPS's record on this matter, pointing out that the open prison regime is based on trust and plays a "very important" role in rehabilitation and progression, particularly for prisoners who have served long sentences.
She said that this year 245 prisoners were transferred to the two open centres, the other being Shelton Abbey in Co Wicklow. Eight of these inmates absconded.
"Anyone who has been sent to an open centre has been risk-assessed as suitable and is not deemed to pose a threat to public safety," she said.
"These are prisoners who we can work intensively with before their release and reduce the risk of their re-offending."
The IPS said that pre-Covid there was an average of 400 prisoners each year in the open centres and around 4pc absconded.
The number of prisoners fleeing jail has fallen significantly in recent years, from 187 in 1999 to 140 in 2007 and only eight this year.
Since being appointed three years ago as the first woman to lead the prison service, Ms McCaffrey has regularly raised concerns about the challenges of the large increase in mentally-ill prisoners being housed in jails, but says the situation is being tackled.
The jail system is dealing with 140 prisoners who have schizophrenia out of a total jail population of 3,774.
In relation to personality disorder - which is not deemed a mental illness under the Mental Health Act, but is a condition that causes problems in jails - Ms McCaffrey said that in the general population the prevalence of this condition is between 4pc and 11pc, but in the jail system between 60pc and 70pc of prisoners suffer from it.
"Despite incredible efforts by our staff dealing with vulnerable people with significant problems, the reality is we cannot provide the treatment they need in our setting," she said.
The problem is so severe that there are 11 men and one woman in prison who are on a waiting list to be accommodated and treated in the Central Mental Hospital (CMH).
A new, bigger CMH is due to open next year, but Ms McCaffrey believes it will not have the capacity to provide for the number of mentally ill prisoners in the system, with only six extra male beds and 10 female beds being provided in the new facility.
She pointed out that, as part of its budget for next year, the IPS has been granted €2m to deal with the issue of mentally-ill prisoners.
The service has received international recognition for how it has successfully dealt with the Covid-19 crisis, with only one death in custody from the virus since the pandemic began in March last year.
The deceased was a convicted murderer from Cork, who died last month.
With more than 85pc of all prisoners fully vaccinated, Ireland has the highest vaccination rate of prisoners in Europe.
Ms McCaffrey said that despite the pandemic, the prison system is operating normally, with classes, visits and mixing among inmates now in place and twice-weekly antigen tests being carried out by all prison staff.