As a rule, these sales reps dole out loads of samples of drugs, particularly those new on the market. We give these samples to our patients, who then report back to us on whether these drugs work, or in fact work better than their old drugs.

Mirabile dictu! Some of these drugs really may be better than other drugs, which logically leads physicians to start prescribing them. Other drugs don’t work as well, and therefore are left in the dustbin.

My point here is that mere sales pitches would not influence physicians, as a rule, to start prescribing drugs. Experiences with using these drugs, coupled with unbiased information about them from reliable sources,
usually dictate physicians’ decisions on whether to prescribe them or not. This is not to say we don’t have physicians who are vulnerable to these sales pitches; we do have a few of them but are most likely the exceptions rather than the rule.

As for DTC advertising, drugs are hawked in a manner that appeals a lot to common folks, particularly with their usually extravagant promises of being top-notch drugs that “most doctors recommend.” (Have you seen those ads for Crestor and Advil? Make you sick, right?)
In my experience, I have never been swayed by these cheap and misleading ads, and my patients usually understood the nature of those ads once I explained why they are there.

In sum, marketing schemes by drug companies work to a certain extent; collectively, as noted by DB, those could translate into billions of dollars. Big Pharma, after all, would not spend close to 40% of its sales revenues on marketing if it does not work.