It will give the effect of being under the influence of Amphetamine, also known as speed. I recommend you do not attempt an ADHD medication if not diagnosed with it by a Licensed professional.
Part two: Not only that, but you may become anemic and dramatically underweight, can approach death as a small child, and become depressed (personal experience from improper diagnosis of asperger's).
I have adult ADHD and I once had a roommate that did a ridiculous thing. She did a self-diagnosis and determined that she had ADHD. She stole around twenty of my Ritalin from the cabinet that I place my medication in. She left to go camping and decided that she would take the amount that had been prescribed by my doctor for me. Well, to make a long story short, she ended up in the emergency room. She started to display symptoms of a heart attack. I strongly advise individuals that think that they might have ADHD to consult with a specialist that will make a well researched diagnosis. I believe some people out there "wish" they had ADHD. I will be fifty one in a couple of weeks and have had ADHD every since I can remember. Having ADHD presents many challenges in a person's life. Individuals have to learn compensatory skills to overcome many of the obstacles that they face. I have encountered many "normal" people who greatly misunderstand me. I have even been called "weird" by neighbors, friends, and colleagues. Despite, all of this, I went to college. I have a Bachelors in Science (Magna cum Laude) and a Masters of Education (Summa cum Laude) degree in the field of special education. I taught severely disturbed children for twenty-eight years. I have retired from teaching and am currently enrolled in a Solar Photovoltaic program. Whenever I become discouraged I think about a quote that Montel Williams made at the beginning of his career: "Believe to Achieve."
So in short, if you're not diagnosed with ADHD, there's no reason to take such medication.