a front - Getting drugs with a promise to pay later, like you're going

Getting drugs with a promise to pay later, like you're going to remember your debt when you're high.

"He got drugs and said he'd pay me later, but I know he won't remember,"

"She got her drugs, and she promised to pay me, but I know she's broke,"

"He got the drugs, and he said he'd pay, but he's just going to forget."