Ganglion cysts usually do or don't need to be injected with medicine?

Usually don't. Many people have ganglions which are never treated. It is only if they become painful people will seek medical help. Depending on the location of the cyst you may want to see if a cortisone shot will help but I have found they will usually return. Excision of the cyst is usually your best bet for permanent removal with only a 5-10 percent chance of recurrence.
Yes. Most physcian inject steroid after aspiration of the gaglion cyst. Thank you.