Equally comfortable at fly-half or full back, Drahm holds a number of kicking records in the Guinness Premiership as one of the league's top ten marksmen in history and last season smashed through the 1,000 point barrier.
The 30-year-old, who has represented England A after qualifying through residency, has also enjoyed spells at Queensland Reds, Bristol and Northampton Saints.
Hickey, 29, first moved to England in 2002 when he joined Orrell before a switch to Worcester the following season.
The Australian Sevens star was a key component of the National Division One winning side and the back row ace has been crucial to the club's development in the Guinness Premiership.
"Shane and Drew have both been great servants to Worcester Warriors, an important part of our development and remain key part of the first team squad this season," said Mike Ruddock.
"After contractual discussions, Shane and Drew have decided to do what they feel is right for them at this time in their careers.
"We wish them every success in Japan whilst we will now explore other options for the back row and fly half positions next season."