Cheat ultimately regrets hesitations means to stop lying (10)

I haven't cracked this one yet — but the brilliant team at Fifteensquared have:

Last letter (ultimately) of [chea] T , then RUTHS (plural of ruth = regret or repentance), then ER + UM (two sounds expressing hesitation). A drug that purportedly forces the recipient to tell the truth; it’s a convenient idea, but such things have never been proven to work.