The relatively obscure profession of “detailing”–in which pharmaceutical reps schmooze with doctors in order to get them to prescribe their employer’s drugs–seems to have exploded because of another little-known practice called “prescription tracking”. That’s when pharmacies sell information on which drugs each doctor prescribes to data-mining companies like IMS Health Inc., which process it and sell it to drug makers.

Many doctors don’t even know it’s happening, but the information revolutionized drug marketing. It’s a powerful tool for detailers to tailor their message to each doctor’s prescribing habits, former detailer Shahram Ahari told the Straight. They can also use it to reward high prescribers while withdrawing benefits from uncooperative ones.

Since IMS launched the first prescription-tracking service in 1993, drug-marketing spending and the number of detailers in the U.S. have both tripled.

B.C. is one of the few places in Canada or the U.S. to prohibit pharmacies from selling doctors’ prescription details. A growing number of U.S. states are following suit as concern grows about drug marketing. New Hampshire and Maine have adopted laws similar to B.C.’s, and others have banned gifts, put limits to their value, or required them to be disclosed publicly.

More than a dozen other states hope to ban prescription-tracking, but those efforts are now on hold because data-mining companies have challenged the restrictions in court as unconstitutional. Judges have so far sided with the companies. A New Hampshire appeal ruling is expected in coming weeks that could open the door for more than a dozen states now contemplating similar laws.