Hypodermic needles and syringes are big, and the volume of fluid needed to be injected is around 1 millilitre. Even using the smallest needle size which is 25 gauge they are very easily bent and still sting when the skin is penetrated.

To get through layers of clothing the 25 gauge needs to be long, not a short one that diabetics use. After injection if not directly into a vein, it can take up to 40 minutes for the drug to take effect.