The thing about overdosing is that it can be different for different people. What I mean by that is an amount that doesn't cause any adverse effects for one person might actually be too much for another and cause overdose symptoms.
I had overdose symptoms from gabapentin the first couple of times I took it when it was prescribed to me for pain relief. I didn't take more than I was prescribed but since I had never taken it before, it made me really dizzy and sleepy. After a couple of days though, the overdose symptoms went away even though I didn't adjust the dose at all.
So I think it's important for people to get to know themselves and how their body tends to react to medications. It's always better to start out with a lower dose of medication and work yourself up to the prescribed dose to avoid overdose symptoms. This is just my opinion, I'm not an expert on this subject.