The conclusion of the first study was, "which could result in further decreases in dopaminergic signaling when the individual with ADHD is not medicated (i.e. over weekend holidays)." duh, of course you will have less dopaminergic signaling when you are off the medication. The whole reason you are on it is to increase the signaling. Also, it was billed as a long term study - and it lasted one year. Many, many people have been on the medication for years and years and years will no ill effects.
The second study dealt only with rats who do not have ADHD. It is true that if you abuse stim meds you will have problems. Thats why it is so difficult to fill your perscription. Read the comments by Michael Sheehan below the article to see why it doesn't apply. And nothing in the last link talked about damage to brain cells.
In short, ritalin has been in use for at least 35 years. If there was any long term effects, it would easily have been noticed by now. What has been noticed by the way, is what happens if you do have ADHD and don't get proper treatment (meds and behavioral modification techniques). You self medicate, and tend to have much more depression and anxiety then the person who got treatment.
I would really love to see that study or a link to it. I get updates on adhd research and I have never seen this study or anything like it. In fact, I can't conceive how it could be anything but a casual relationship and thus invalid. So would really like to know more about it, and where it appeared (a "Natural" news site?)
In answer to your question. Kind of sounds like you are depressed. Depression is a known co-disorder of ADD/ADHD and is many times caused by AD/HD. So if the AD/HD is not being treated, the depression returns.
Oh! I assume that you were prescribed Concerta because you were diagnosed with AD/HD?
Are you getting a good nights sleep? Are you finding it harder to fall asleep since going off the Concerta?
Yes I was diagnosed with ADHD. My sleep has always been good even with Concerta. If I am depressed, I am not more depressed now than I was before but the difference is my personality.
Here are the studies that suggest long term effects, let me know your thoughts. They are mostly for Ritalin http://www.medicaldaily.com/long-term-ritalin-use-adhd-may-worsen-symptoms-and-reduce-drug-efficacy-245927
http://www.thefix.com/content/research-shows-ritalin-causes-long-term-brain-injury. . http://www.drugs.com/sfx/methylphenidate-side-effects.html