I didn't know what Focalin was, so I looked it up: Focalin (dexmethylphenidate)
Hmmm... Ritalin and company are: methylphenidate
In other words... Focalin is a modified version of the same chemical composition that is in Ritalin, Concerta and so on.
Modified means it may have slightly different side effects, time window, etc.
I'm more familiar with Methylphenidate, including having used it myself.
Methylphenidate - at least in our area - is the most common initial medication tried for ADHD. It's been around for a LONG time. Unless you get a really atypical reaction, most side effects are mild, and go away when the drug is discontinued... including appetite suppression.
The fast-acting form has about a 4-hour window (in real life, somewhere between 3 and 5 hours... it is never as accurate or scientific as the scientists want to believe, when it comes to "effect"... they can prove how many hours before the medication is physically out of your body, but not how long it is effective for)
Our kids started on this medication at 5 and 6... and the results were and still are obvious.