Do you for something like an automatic weapon? Well, I had the same problem, Mouse>Button Is Down>System Create Object>Bullet
And that would spam the creation of bullets. So what did I do? Well, I created a global var named "CanShoot", then for the first event, I did:
Mouse>Button Is Down>System Create Object>Bullet
>System>SetValue>CanShoot to "false"
Then I added a condition to the Mouse>Button Is Down for checking if CanShoot was true or false.