Its really not that unusual for adhd kids to lie. Stats show that almost 50% lie (compared to about 7% normal kids). I've posted countless times to parents saying don't punish your kid for lying since most of the time it due to their ADHD conditions. Try googling "lying and adhd" and you will see pretty good explanations of why it happens.
If you understand what adhd is and its effects on you, it becomes a lot easier to deal with those effects. I can give you many good resources if you are interested. A really good one that I saw recently is the totallyadd.com website. It's aimed at adults. Another good one for adults is http://jeffsaddmind.com/for-first-time-visitors. Both of these sites are written/produced by adults with ADD and have a lot of helpful ideas.
For you, I would think that if you can understand the the lying you do is probably to cover up the mistakes you make due to ADD. You are on your way. There are many tricks of the trade, that you can use to cut down on these ADD type of mistakes. Sites mentioned above will cover many ideas. Also take ownership of yourself. Admit you screwed up. My last school principal (before I retired) was totally ADD-maybe ADHD. She couldn't focus on one thing for more than about 4min. But, oh Lord, was she an awesome principal! She knew what her shortcomings were and warned people before hand. If she messed up, she apologized and fixed it. Of course, she also had gotten a strong sense of self confidence along the way, and that really helps.
So read up of ADD. Realize that many of the things that caused you to lie as a child, you now have more control over. But more importantly, you can have a lot more control over yourself - if you want to take it.
This won't come easy. Many people with ADHD have a loss of self confidence gained through all those years in school. But each time that you stop, and say, "ya, I messed up. I'm sorry. I'll fix it" You will feel better and that self confidence will start to grow. If you start using some of the coping skills the web sites mention to cut down on these mistakes, then you will really start feeling more in control and the self confidence will really start to rise. Hope this helps. If you have any more questions, please post!
Would you be willing to get some outside help with this?