Last month Stevenson admitted his role in producing and supplying Etizolam and smuggling a tonne of cocaine – which police estimated would have been worth £100m on the streets – into the UK.
Five other men – David Bilsland, 68; Paul Bowes, 53; Gerard Carbin, 45; Ryan McPhee, 34; and Lloyd Cross, 32 – also pled guilty to serious organised crime and drug offences.
Carbin was jailed for seven years; Bilsland, Bowes and Cross were all jailed for six years; and McPhee was jailed for four years.
Lewis Connor, 27, was jailed for three years in July after the investigation found encrypted phone messages which proved he had set fire to properties and vehicles across Central Scotland.
The drugs operation, which spanned the UK, Spain, Ecuador and Abu Dhabi, had been targeted by police in an inquiry which was named Operation Pepperoni.
Officers had been investigating reports that Bilsland, a Glasgow fruit merchant, had links with organised crime. He was then seen meeting Stevenson in a hotel in Spain.
At about the same time, officers had learned that Stevenson was involved in setting up a factory in Kent which was producing millions of Etizolam tablets.