Assam Police Special Task Force (STF) intercepted a vehicle in Kamrup district early Monday, seizing 40,000 Yaba tablets that weighed 4 kg.
The operation followed intelligence that a consignment from Mizoram would transit through Amingaon into Lower Assam, a route that has long served as a conduit for synthetic drugs from Myanmar.
The carrier, Md Hakim Dewan, 36, a resident of Barpeta police station, was taken into custody. STF officer Rajesh Kumar said the arrest was a decisive blow to the drug network.
The tablets are estimated to be worth Rs 10 crore on the street, but the CID rate list puts the value at Rs 6 crore.
Mizoram has long been a key entry point for synthetic drugs into Assam, and local residents in Kamrup say the crackdown has eased their fears after a boy in their village fell victim to Yaba addiction.
Legal proceedings will commence under the Narcotics Control Act, with a trial scheduled for September 15 in Guwahati.