Get a second opinion, though adhd could be a contributing factor. Also, could he perhaps have sleep apnea? It seems treating the depression, getting him on a good diet and excersize routine could help. One other thing, too much sleep can also cause drowsiness.
In the meantime, I ran across this article today, some things may help him to at least distract and wake him up some:
5 Ways to Beat Fatigue at Work
Try these 5 easy tricks for jump-starting your energy when you feel like you're on the verge of dozing off...
http://health.msn.com/nutrition/slideshow.aspx?cp-documen...
1. Eat a Tiny Square of Chocolate
Chocolate has been shown to not only boost our mood, but eating it helps the body release energy-boosting feel good endorphins. When I'm about to fall asleep in my chair, I have a little square antioxidant-rich dark chocolate. Does the trick.
2. Drink Two Small Glasses of Cold Water
Not huge glasses--little cups will do. Here's why: One of the major causes of exhaustion is dehydration (sometimes you don't even know you're dehydrated; instead you just feel sluggish). A high school teacher of mine used to have us drink two cold glasses of water after lunch in calculus class, and I swear it kept us going through that boring hour. Go rehydrate your cells right now!
3. Doodle
If you're yawning and having trouble concentrating on a conference call, consider pulling out a pad of paper and a pen and letting yourself doodle a bit--that's right, hearts, unicorns, rainbows ... whatever goofy thing comes to mind. I recently interviewed an expert for a magazine article who told me that doodling can help the brain focus. So surprising, right? And when you're focused on what you're doing, you're less likely to be zoning out and thinking about a nap.
4. Snack on Something Vitamin-C Rich
Slice up an orange or run out for some lemonade at the cafeteria--the point is, get a bit of C. Past studies have correlated C with vitality and even reducing the symptoms of chronic fatigue syndrome. Worth trying!
5. Stretch
A simple forward bend, according to Chinese medicine, can activate a reserve of sustaining energy that rests between the kidneys.
6. One thing I do, is stand up, walk down the hallway, crumble up a piece of paper and go throw it in a wastebasket or recycle bin across the room, just something to get me out of the seat for a moment.