system
Given the following post, respond as if you're commenting on Reddit:
human
What happens to a non-diabetic when given a shot of insulin?

I get asked this question regularly so I was wondering if anyone can point to an answer.  I would think they would be able to decrease the amount of insulin produced by their own body but this is just a guess.
gpt
It would depend how much was given and under what circumstances. Insulin is produced in response to detection of elevated blood glucose, there is no feedback based on the level of insulin itself. 
A few units of short acting insulin given to someone who just ate a meal with carbohydrates would have no problems. The injected insulin will lower the blood glucose and the pancreas will make more if needed or none if the glucose level is too low.

What if you gave a few units of short acting to someone who hasn't eaten all day? In that case you might drive the blood glucose low enough to cause brain damage or kill them. The brain is one of the most glucose sensitive organs, and damage occurs quickly if it gets too low. Low glucose in starvation is different in that there is some ability of the body and brain to switch to tolerate lower glucose by partially using other metabolic pathways. Switching take time though, so fast drops in blood glucose are dangerous.

Long acting insulin could do the same thing as giving short acting insulin to a person with low blood glucose. Eventually the food they ate is digested, but the long acting insulin sticks around and blood glucose will continue to decrease until they get into trouble.

The low glucose (hypoglycemia) causing brain damage and coma is one of the reasons killers sometimes use insulin to kill people. Usually diabetics that they switch the dosing on so it looks like an accident.

Too high a glucose level is actually short term pretty safe. That's one of the reasons why unconscious people get intravenous glucose with electrolytes. Too low is much worse than too high, and the lost time to check can make a difference in recovery.