Flying with syringes. United's policy.

[frorider6]

I had no problem with having 4 pre-loaded Fina syringes in my checked luggage. Basically, you can't carry any with you unless you have a prescription, but there's nothing that says you can't have them in your checked bag. They just don't want you to be able to use the syringe as a weapon.

I had no problems and even flew back with the empties because I didn't want to dump them irresponsibly.
United's policy

Dangerous objects not allowed in the cabin
No knives of any length, or made from any material, are permitted in the cabin of an aircraft. (Plastic knives are permitted for meal services.) Cutting instruments of every kind are banned, including but not limited to, carpet knives, box cutters, knives with folding or retractable blades (regardless of blade length), steak knives, straight edge razors, ice picks, and metal scissors with pointed tips. Other prohibited items include baseball bats, golf clubs, pool cues, ski poles, and hockey sticks.
Medically necessary needles and syringes are exempt from these prohibitions if passengers have in their possession prescription medication with a professionally printed label that identifies the medical office, pharmacy, or manufacturer of the medication.

Just be responsible about it. Mine were in a hard case, inside my shaving kit. No chance of the pin working loose and sticking out of the bag.