Baker Bros has one of their own on the board of directors, as well as enough voting stock in the company to steer the company in the way they want it to go now. So there is nothing for them to gain by attempting to buy the company. And don't forget this company is 93+% institutionally owned, so any one trying to buy ACAD would have to pay a very steep price
It is not their style to take a company private. Their average holding period is 3-5 years. If anything, they would be instrumental in getting the best price for their shares, should an offer be tendered.
With all due respect, if Baker Bros wanted to take Acadia private, they would have done it at $8 or $12, they would not have waited until the stock was at $21 and paid a $40+ number.
Keep in mind that 'inside' LBOs get an incredible amount of scrutiny re fairness of terms, e, g, Michael Dell/Silverlake.
If an insider tried a buy Acadia, the BOD would appoint an independent sub committee of the BOD. This committee would most likely hire a 'tier one' investment banker to 'shop' the company to dozens of potential buyers to get the best price. (I mean a full Offering memorandum of several hundred pages with all support docs available after a bid is received.)
This IB firm gets paid a much larger fee (by millions) if they can find a higher bid vs. the 'consultation' role, so they have tremendous incentive to get an 'over bid' to an insider offer. They would also be providing a fairness opinion to the BOD and have potential liability if their is a SH class action.
For all of the above reasons, I seriously doubt a BB takeover will be proposed, and if it were, we would still see the company sold to the highest bidder at the best price IMO.