Ten thousand pills were found in the boot of a car carrying three Bradford men.
The grey Vauxhall Vectra was stopped by Cumbria Police in Carlisle.
Officers found the haul of tablets, stashed in ten tubs, and arrested the men on suspicion of possessing controlled drugs with intent to supply.
A spokesman for Cumbria Police could not say what the pills were or what their estimated value was.
The haul has been seized to undergo forensic examination.
The police spokesman said: “On Tuesday, February 19, at about 9.55pm, police stopped a grey Vauxhall Vectra on the City West bypass at Carlisle, between the Kingmoor South roundabout and the Etterby roundabout.
“Three males were inside the car and as a result of it being searched, officers located ten tubs of small tablets, estimated to have contained somewhere in the region of 10,000 pills, in the boot of the vehicle. “Police suspect these to be illegal and the three men – all from Bradford and aged 31, 32 and 34 – were arrested on suspicion of possessing controlled drugs with intent to supply.
“The car was seized by police for further investigation.”
All three were taken to a police station to be interviewed and were later released on police bail until May 20, pending further inquiries.