So you've thought it through and come to a decision: your dog might benefit from medicine as a tool to treat his behavior problems. Now you will need to see a vet, since (in the United States, anyway) only vets can legally prescribe medication for a dog. Don't make that appointment yet, though! Just like with humans, you have options. Today, I'm going to outline what some of your choices are.
A board-certified veterinary behaviorist.
A board-certified veterinary behaviorist is much like a psychiatrist in humans: they are vets who have gone through a rigorous certification process in animal behavior. Identifiable by the initials DACVB after their names, these vets have three years of post-vet school education. They complete a residency, conduct and publish original research, submit case reports, and pass a two day exam. In other words: they are highly educated, and highly experienced.
I personally think that veterinary behaviorists are the gold-standard, and when Maisy and I pursued medication, we saw one. Unfortunately, they can be hard to find, as there's only around fifty in the US and Canada. (Check to see if you have one near you here.)
A vet who is not board-certified, but does have some credentials in animal behavior.
There are several other organizations that certify animal professionals in some way, although they accept any qualified person, not just vets. One such organization is the Animal Behavior Society, which requires its behaviorists to have completed either a Master's degree or a PhD in behavior or ethology, pass oral and written exams, publish articles in scientific journals, and complete supervised experience. Once these criteria have been met, the professional can designate themselves as a CAAB- but remember, they may or may not be a vet, so check their credentials carefully. (You can find one near you here.)
There are other certifications out there, as well (and feel free to comment if you know of some). In addition to assuring that your chosen professional can prescribe meds, you should find out just what vet had to do to obtain the certification they have, and then decide if that means they have the knowledge and experience you want your behaviorist to have.
A vet with a special interest in behavior, but no particular certifications.
Don't let the lack of a certification dissuade you- there are definitely vets out there that really enjoy doing behavior work. They likely have obtained continuing education credits in animal behavior and read journal articles. They might even have a specialty practice in behavioral medicine.
Unfortunately, without any certifications, they can be hard to find. I googled up a few in my area, but it took a lot of work to sort through the results to find actual vets. And even once I found them, it was hard to know what, exactly, qualified them to do behavior work.
Any general practice vet.
Any vet can prescribe medication, so you certainly can make an appointment and request behavioral drugs. Unfortunately, their knowledge of behavioral drugs might be rather limited... and it's possible they are even lacking in general behavior knowledge, too (vet schools generally require little in the way of behavior coursework).
While they may not have the same breadth of experience and knowledge that vets specializing in behavior do, they can certainly be an affordable option- and if you live in a rural area, this may be your only option. It's also more likely that you'll have developed a relationship with this person, which can go a long way to helping you feel at ease.
Finally, you can do distance consultations by phone, fax, or email. Many veterinary behaviorists will consult with your regular veterinarian regarding medications, while others, like Tufts, offer a remote consulting service that allows you to cut out the middleman and communicate with them directly.
So which option should you choose? Well, a large part of your decision will likely be a function of your location and budget. Board-certified behaviorists can be expensive, and they're certainly not common, so it can be hard to find one nearby.
But you should also consider your dog's needs; some dogs are pretty straightforward and will do just fine with a general practice vet, while others have much more complicated behaviors and might need a highly skilled clinician to parse out the issues. I believe that if your dog falls into one of those proceed with caution categories, you'll want to hire the most experienced and knowledgeable person you can find.
Finally, no matter who you're inclined to go with, you need to do your research. Find out how much experience your intended professional has. Get some recommendations. Educate yourself, and be your dog's advocate. Ask questions during the appointment, and make sure you have a plan for follow-up.
Does your dog take medication? What type of vet did you see? Why? Were you happy with the results?