It flows no problem. Some people have prblems with infections from 25 guage because they 1) tend to shake the needle more while injecting because of the slower rate / harder push and 2) because 25 guage only comes in 1 inch length. some people need the full 1.5 to get deep enough into the muscle. If you start to have a problem with infections, drop back down to a 23 X 1.5 and try that.