Will Parelli calm him down?

I see, thanks for the response

If he was undernourished and is now well fed and underworked that could certainly be adding to his behavioural issues. Can you tell me what he is being fed and how much work you are currently doing with him?

As for being drugged, before you jump to that conclusion, let me share a story with you:

I recently moved my own TB mare to a new barn. For the first week she was an absolute angel. Then she decided one day that it was just all very scary and began to act out in various ways. It is now almost five weeks since the move and in those following weeks I have worked with her consistently to re-focus her attention to me first, and environment second. Slowly and surely the results are becoming apparent, but it takes work!

I am sharing this with you because if I didn't know this horse, and know for a fact that I didn't drug her, I would have sworn that she was drugged given the initial calm attitude followed by a complete behavioural change. It can, and does, happen.

It is going to take time and patience to work with your boy, if you do not have a 'bag of tricks' so to speak in your training repetoire you will certainly need to begin a quest to find such techniques. Parelli is one place you can learn from, there are many others also. I would suggest that having an experienced person, preferably one that has dealt with OTTB's before, is going to be the best way forward.

All the very best with the training and the thrush recovery and keep posting on here for advice and ideas, there are plenty of people that will be happy to help!

I would MUCH rather have two sessions a month with a trainer (that would run around $60-70/month where I live) than any number of DVDs.

DVDs can be nice background info, but are no substitute for reading an individual horse and having a specific training plan for the next week or two. A good trainer can also help you find out what YOU don't know...

I agree about the feed. I'd try reducing any grain or supplement until he is on just hay and see if he's so energetic. It will take several weeks or more to find out. While he has the thrush this is a good time to work on his "standing" manners. Not cross ties, just voice command. Tell him stand and put him back on the same spot with the command to stand every time. Be patient, he'll eventually get the message that he's to stand when he's told to.

I too would not jump to the drugging thing.

Make yourself a list of everything that is different in how you keep him than how his previous owner kept him.
Include amount of turn out. Feed (type and quantity). Amount of work.
Everything.

There are so many variables that can affect a horse's personality. A simple change in daily routine can change a was quiet horse to an overly anxious horse.

Frequently the variable is something as simple as a feed change. Some horses do not maintain their brain on certain feeds. So what if every other horse in the barn does fine on it.
Some horses like a very strict work schedule and get silly if instead of one day off they get two.
Some horses do not like bugs so much that if their turn out time changes from early morning to late afternoon they are a basket case.