Possible Clues:

• Numbing drug
• Pusher's product
• Stupor-producing drug
• Inducing sleep at last, spin concentric circles?
• Drug flowed up opening in centre of the ear
• Went back to bed, one originally called number
• Scurried up to bed with current cold with the equivalent of one of those in 21 across
• Numbing cold crushing Scott's heart, Amundsen ultimately coming first
• Worked backwards, 101 to 100 ... after retiring, it could put you to sleep
• Drug baron's end: caught with nothing stashed in lorry?