Police launched a series of raids in Renfrewshire after Border Force seized around 4,000 ecstasy tablets.
The joint operation, which involved Police Scotland and the UK National Crime Agency, targeted premises in Barrhead and Paisley.
It followed intelligence that criminals were using the postal service to import controlled drugs into the UK.
The NCA confirmed the haul of Class A drugs had a street value of about £40,000.
Two people were arrested and later released while investigations continue.
NCA senior investigating officer John McGowan said: "Working with our law enforcement partners we are determined to do all we can to disrupt the criminal networks involved in drug importation and supply."