A related topic, including a study, reusing syringes.
A famous doctor who reuses syringes
On himself, not on his patients 
But he does provide some detailed directions for patients who do want to reuse them. This is a quote from the latest version of Dr. Bernstein's Diabetes Solution: The Complete Guide to Achieving Normal Blood Sugars
He has more information about reusing syringes in his book but I wanted to quote this part. At the end of the quote, he mentions that he reuses syringes.
If you would like to see a video of him doing it, watch this one about injecting into a muscle. The information about muscle injections is very useful, and I've never heard another doctor talk about it.
It is an older Google video, and can't be embedded on the site, but here is the link. Dr. Bernstein explains how and why to give yourself a muscle injection.
Notice that he demonstrates twice using the same syringe, and what's the harm in that?
Another video with Dr Jason Baker demonstrating insulin injections. He injects 3 times with the same needle. That part starts at the 5 minute mark, but the other comments are interesting too.
And an interesting case of a diabetic rancher using a syringe for more than a year. The cattle syringe.
It's a bit of a peeve for me, but if you mention reusing syringes, people go "eek!" If you mention insulin pumps, the reaction is "wow, technology." But insulin pumps are responsible for many more infections than are caused by syringes.
If you are going to puncture the skin, there is some risk. It is extrmely small with either new or reused syringes. The largest study on reusing syringes had a very lopsided score. Over half a million injections, zero infections. Insulin pumps depend on keeping the feed in the skin, and the infection rate increases.
That isn't to say that insulin pumps shouldn't be used. People are so different. For some diabetics, pumps are very much appreciated. There are good practices recommended to keep the infection rate down.
If you are reusing syringes, keep the end cap on at all times when the syringe is not in use. You do not want to share the syringes with another person. The reuse is only for one person.
Some insulins are not meant to be mixed with any other type of insulin. Use a different syringe for Lantus, or for other types requiring it.
Dr Bernstein also doesn't change his lancets unless they get damaged or dull, and he mentions to his patients that this isn't needed. Neither he nor his patients have ever had an infection from reusing lancets.
A related topic, including a study, reusing syringes.
