The Answer
Now, back to our original question. Does the tryptophan in turkey make you sleepy after eating a big Thanksgiving turkey dinner?
Sorry to say, that if you're looking for the sedative effect, it's unlikely you'll get it from eating meats like turkey. L-tryptophan doesn't act on the brain unless you take it on an empty stomach with no protein present. So it probably isn't at fault for the sudden drowsiness that hits right after the meal when the football games come on, and the dishes are waiting!
It's more likely due to the combination of drinking alcohol and overeating - not just turkey, but also mashed potatoes, ham, creamed onions, cranberries, sweet potatoes, peas, stuffing (or dressing, if you prefer), carrots, bread, pies, and whipped cream - all of which have the effect of puling the blood away from your brain to help your digestive tract do it's work, and the sugar/insulin effect.