In nursing school we were told that infants didn't really need pain relief for needlesticks, IV starts, circumcisions, and other painful procedures; they just needed a pacifier dipped in a heavy sucrose solution. The sucrose solution elicited a sort of euphoria which blocked the pain, and possibly amnesia about the event so they didn't grow to feel rejected and abandoned in a hostile environment.
What a load of crap, we all thought. None of us believed it. I don't think the nursing instructors even believed it. There's not even a good physiological explanation for it. Yet it's a thoroughly established practice.
An interesting article from Peaceful Parenting highlighted a Lancet published study which showed that oral sucrose doesn't block pain in infants. Rather, it occasionally changes their facial expressions, which alters the caregiver's impression of their pain. Spinal cord pathways and brain activity related to pain reception did not change whether infants were given sterile water or sucrose solution prior to a painful procedure. Other infantile reflexes related to discomfort were not significantly different, either.
It's nice to see non-evidence-based practices being knocked down. However, I think it might be a long time before busy obstetrical and neonatal clinicians take this study (or, in general, the effects of pain on infant bonding, feeding, and neurological development) very seriously.