Large quantities of counterfeit drugs were seized in a co-ordinated series of raids carried out on both sides of the Border early on Saturday
The operation code-named "Nora", was part of a clamp down on the distributers and manufacturers of illegal animal remedies.
The raids on farms, homes and businesses involved over 100 gardaí in the Republic and the same number of PSNI officers in the North, backing up teams from the Departments of Agriculture and Health.
A raid in Co Tyrone uncovered an illegal animal drugs manufacturing plant and a large quantity of counterfeit drugs were seized.
In the Republic, 10 separate raids were carried out in Counties Carlow, Waterford, Monaghan and Cavan, with teams which involved the National Bureau of Criminal Investigation. In these raids, thousands of Euro worth of antibiotic drugs, counterfeit veterinary drugs and two diesel laundering plants were uncovered.
At a number of the sites raided quantities of stolen goods were also found. No arrests were made but files are being prepared for the Director of Public Prosecutions and the Chief State's Solicitors Office.
The diesel laundering plants were uncovered in Co Monaghan and Co Waterford and illegal veterinary medicines were found at all the locations.
Operation Nora was planned by the Special Investigations Unit of the Department of Agriculture and Food and the preparations took months.
Sources close to the Department of Agriculture and Rural Development in Northern Ireland expressed delight at the uncovering of the illegal animal drugs factory at the weekend.
The source said that over the past year, a flood of counterfeit drugs had been coming on to the veterinary medicines market and this had been noticed on both sides of the Border.
"We seem to have located the source of one particular drug, a wormer, which of course, has never been tested or passed as safe for use in food animals and do not have marketing authorisation which is issued by the UK Veterinary Medicines Directorate," he said.
A statement from the Department of Health, Social Services and Public Safety, confirmed its personnel had carried out the searches in Cos Down, Tyrone and Fermanagh.
The searches, it said, were carried out in conjunction with the Department of Agriculture and Rural Development and the Police Service of Northern Ireland.
"It is the view of the Department that the use of illegal veterinary medicines could have detrimental implications for human health through the grown of antibiotic resistance and contamination of the food chain," said a DHSSP spokesman.
"Such unregulated use could have a devastating effect on the agricultural industry. The Department, in light of such threats, is appealing to any person who has any information regarding the purchase, sale or use of such illegal medicines to contact us," he said.
There is a growing trade in counterfeit veterinary medicines on both sides of the Border over the past couple of years as the drug dealers have turned away from selling illegal growth promoters because the detection rate is so high.