Are monetary kickbacks common? No.

Are incentives in some form or another (trips, meals, merchandise) common? In the United States, yes.

Do Medical Doctors receive kickbacks from pharmaceutical companies?

Yes. It's called bundling.

Yes, they do, and its in cash. What they do is fill out questionnaires, and get reimbursed.

When the Pharma sales reps take the Dr. and his whole staff out for lunch 3 times a year, do you think his companies drugs are going to be prescribed more often by that Doc ?

of course

Kickbacks are rampant in the field of Psychology. If you look in a doctor's office, you see ads all over the place. Pens, pads, posters, all with their favored medication of choice emblazoned everywhere.

They also tend to own stock in the pharmaceutical companies which they prescribe to.

Unlike the MDs, psychiatrists don't even attempt to hide bias in prescribing.

Of course, if you're smart like I was in residency, you just take the free food, free trips to conferences, etc. and then prescribe the drug you think actually works, regardless of who gave you what. You get free stuff and you still treat patients effectively =).