Ecstasy with a potential street value of £2m was recovered in an operation by the National Crime Squad and the Central Motorway Police Group.
West Mercia Police was one of four forces involved in the seizure, the others being Staffordshire, Warwickshire, and West Midlands.
A total of 200,000 tablets were found hidden in the boot of the car after a man was stopped on northbound carriageway of the M6 between Junctions 5 and 6.
It is believed that the seizure on Monday represents one of the biggest of its type ever by police in the West Midlands.
The CMPG polices the Midland region motorway network and comprises officers from each of the four forces.
"The prompt actions of the Central Motorway Police Group in stopping this vehicle resulted in this major seizure of what is a Class A drug," said a National Crime Squad spokesman.
The Birmingham branch of the Squad is now liaising with colleagues in the Scottish Drugs Enforcement Agency over the investigation.
A man has since been charged with possession with intent to supply ecstasy.
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