The Riders said in a statement that the positive sample was collected last November during a random test.
“We are disappointed in Marcus and that he has tested positive for a banned substance,” Riders general manager and head coach Chris Jones said.
“We have been in conversation with Marcus and the CFL for clarity and accept the leagues decision and corresponding two-game suspension.”
The league said Thigpen tested positive for Dehydrochlormethyltestosterone, which is also known as Oral Turinabol, an anabolic-androgenic steroid.
A suspended player is not allowed to take part in regular or post-season games, but is eligible to play in pre-season games, and participation in other team activities is at the discretion of the Riders.
Thigpen signed with the Riders in September 2017 and played two regular season games, rushing for 32 yards and one touchdown on seven carries. He also caught two passes for 31 yards and a touchdown.
In two playoff games, Thigpen rushed for 203 yards and one touchdown on 22 carries, and caught two passes for 16 yards.
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