My understanding (and it's relatively poor even though I take Concerta myself) is that the mg is the total dosage that will be gradually released from the XR capsule over the day - so for the majority of the day (especially in the morning) you're feeling far less than 18mg of methylphenidate in active use.

I think this is a discussion to have with your doctor but I'd suggest not coming in overly rationalizing - just tell them how you're feeling on the dose (i.e. it's less impactful) and see what they suggest.

Personally, I've found a different efficacy in Concerta vs generic methylphenidate XR at the same dosage and that tracks with my general impression of any neurological pharmaceutical agent... some things randomly work better for some people and violate common expectation or reason because brains are really fucking complicated, everyone is different, everyone has different brain chemistry, ADHD (and all other neurodivergences) are diagnosed by symptom rather than cause, and, most importantly, we really don't have a fucking clue why things are effective and the entire field of neurochemistry is really just vibes based.

I hope you find a good resolution!

If you say Ritalin, you mean the "normal" version without extended release, right? It is individual how many hours Concerta has an effect, but it's roughly 7-10h.

How much mg of Ritalin do you take in 7-10h in total? That is roughly the dosage you need for Concerta.

While you already have your answer, I thought I'd share this for anyone wanting to know a bit more about how Concerta works. The pills themselves use an osmotic-controlled release oral delivery system where part of the dose is given immediately and the rest is slowly given as the drug gets squeezed out a little hole (that's drilled out by lasers!) by osmotic pressure. It's really cool stuff and makes it quite different to Ritalin IR in how it feels and works.

How do you know its not enough?