endodoc, While I take your point about liquid flow during an injection, I've used a thin needle on myself and trust me, it hurts less going in than the normal thick kind. (Cue cheap jokes...) If I were diabetic and injecting four times a day, I'd want the thinnest needle possible; it hurts less, it leaves less of a mark, and you'll have a smaller sore spot leaving you with more room for further injections. I've not heard of a pain-free injection system for diabetes which is why you get companies looking into nasal sprays and suchlike; they know the first person to offer a pain-free but rapid delivery system will make loads of $$.

Needle-less injection devices already exist but they still cause pain because you are forcing something through the skin. Diabetics in particular may experience pain from needles because they are reusing a needle more times than recommended. Modern fine needles can blunt quickly and it won't be obvious when you look at them. So one good way to reduce injection pain is to ask your doctor or, better still, your specialist nurse to find you the thinnest possible needle & then follow the rules on how many times you use it.

US drug companies can tell patients what needles and devices they make; UK companies are forbidden to give out such information as it is considered advertising even if the patient contacts the company. Thankfully US websites give details of what's available so if you or your child have to inject drugs for a medical condition, do some online homework and see if you can find out if thinner needles or alternative devices are available.