Dr. David Belk has clear data on wholesale (NADAC) and retail costs of generic and branded drugs (from GoodRx) and what drives the costs.

Drug stores in half the states are not allowed to tell you if the cash price is less than your co-pay, but the other half of states have laws letting them tell you. You can always ask anyway.

You can find the number of drug prescriptions from each doctor and costs for Medicare patients in at least 2 places, described below. For non-Medicare prices see above.

ProPublica has Medicare Part D cost for each drug: number of prescriptions and total spending. You can get separate totals for US and each state, so you can get average cost per prescription, and for each doctor who prescribed a drug 50 or more times in 2013.

Medicare itself has more complete Part D data. The US and state summary files (bottom of the link) show for each drug: the number of beneficiaries as well as prescriptions and spending, so you can get average per beneficiary (total during a year), as well as per prescription for each drug.

Medicare's detailed files show number of days prescribed, so you can get average cost of a daily dose, as well as each doctor who prescribed a drug 11 or more times in 2013. This info is in 23 million records, without state or US summaries. However you can get good state and national estimates by opening any of their 36 spreadsheets (divided by last name of prescriber) and getting averages there. The average costs do not vary much by last name of prescriber. (Tips for working with large spreadsheets)

Some doctors and drugs typically have 30-day or 90-day prescriptions, which may be renewed all year. Their averages include the cost for each  whole long prescription (30 or 90 days). Docs & drugs with shorter prescriptions only include that lower cost. Medicare's focus seems to be on cutting total costs, not cost per dose.

ProPublica's methodology says it has "retail cost" for these prescriptions.

Medicare's fact sheet gives more detail, saying it includes,

• The total drug cost includes the ingredient cost of the medication, dispensing fees, sales tax, and any applicable administration fees. It?s based on the amounts paid by the Part D plan, Medicare beneficiary, other government subsidies, and any other third-party payers (such as employers and liability insurers). Total drug costs do not reflect any manufacturer rebates paid to Part D plan sponsors.

It does not directly include patients' monthly premiums, though on average those premiums may cover all drugs, administration, and profits.

After seeing which drugs a doctor prescribes, you can find drug safety and effectiveness from the sources at the top of the page.

Most doctors send prescriptions to pharmacies electronically. This is more reliable than hand-written faxes, but two problems stand out:

• Most doctors cannot send, and most pharmacies cannot receive, electronic cancellation orders
• If the patient does not get a copy, the patient cannot check if the pharmacy filled it correctly.

Cancellation orders are crucial to correct mistakes and cancel refills. Patients can overdose when they keep getting the old medicine after the doctor orders a new one. Only a third of prescribers and 40% of pharmacies use software certified to handle cancellations, so less than a third of cancellations can go through. "Electronic health records allow prescribers to stop a prescription, but what many physicians may not realize is that in most cases that directive is not sent to any pharmacy," even though original prescriptions are reliably sent.

Health systems like the Veterans Health Administration and Kaiser Permanente, where prescriber and pharmacy are in the same organization, can cancel electronically. Otherwise only 5 pharmacy chains accept e-cancellations: 

• CVS/Caremark (which handles 23% of US prescriptions),
• ExpressScripts (12%),
• RiteAid (6%), 
• Kroger (3%),
• Wegmans (under 1%). 

Many non-chain pharmacies accept e-cancellation if they use one of 14 software systems listed with a † You can ask the pharmacy which software they use.

No other chain is certified for e-cancellation, such as Walgreens (16% of US prescriptions) and Walmart (7%). Consumer Reports unfortunately recommends Costco and Sam's Club for price (uncertified), Walgreens for its apps (uncertified), and supermarket chains for convenience (only Kroger's is certified). CR should know better.

Doctors can cancel electronically only if their software is certified under "Cancel Rx". Out of 920 systems, only 80 are marked as certified, and usually only the latest updates. If your doctor is part of a large group, you can ask the group to ensure its software gets certified and updated. Individual doctors have little control.

Automatic refills are even more dangerous. When pharmacies call patients to say, "Your prescription is ready," patients and callers do not know whether the doctor recently ordered it or it is a zombie renewal. Costco, CVS, RiteAid and Walgreens encourage patients to sign up for automatic refills, so patients at Costco and Walgreens (two which lack e-cancellations) can get undesired medicine for long periods, thinking their doctor ordered it.

Prior authorization for prescriptions is a system where an insurer tells a pharmacy that a doctor needs to send the insurer detailed information and get the insurer's approval for the prescription. Insurers tell pharmacies, not doctors or patients, when prior authorization is needed, and pharmacies say they have no obligation to tell doctors, though they have the forms and information which the doctor needs, and no one else does. A Massachusetts court says pharmacies must tell doctors, and a doctor says the entire circuitous system of prior authorization for drugs kills patients.

Direct Payments which doctors get from major medical companies (Medicare's site) and drug companies (ProPublica's site) show which doctors have strong bonds with the companies. Patients need to decide if these affect their care. The sites do not reveal profits from doctors' own businesses. Consumer Reports says that when a doctor orders X-rays or other scans, "ask whether he is financially affiliated with" the radiology clinic, since "studies have found that physicians who own scanners or are part owners of radiology clinics use imaging substantially more than others." 

The Journal of the American Medical Association (JAMA) May 2 2017 summarizes a lot of research on how payments from drug and equipment companies affect doctors' decisions, usually sub-consciously.  Where policies change or payments stop or start, average prescribing practices then change. Public Citizen has a less detailed November 2017 update.

Nurses also get payments and meals from drug companies, but only Massachusetts tracks these payments.

Drug companies also have constant access to doctors and give them biased information. A 2012 summary found (emphasis in the original):

• 61% of physicians reported that their own behavior was immune to influence by industry, but only 16% thought that other physicians’ behavior was equally secure
• sometimes the suggestion that such influence exists can be infuriating to them
• The frequency of meetings with pharmaceutical representatives varied across specialties, ranging from two per month for anesthesiologists to 16 per month for family practitioners
• representatives presented only selected, usually positive, information about their products
• In one of the few studies of specific [training] content, 11% of statements in formal lunch presentations by pharmaceutical representatives were found to be inaccurate, all favorable toward the promoted drug, yet only 26% of medical residents attending those presentations recalled hearing any false statement. All statements about competing drugs were accurate, but none favorable
• research supported by industry is more likely to report positive results—3.6 times as likely, according to one meta-analysis
• One study of industry-sponsored review articles and Cochrane [academic] reviews on the same medications found that all of the former recommended the drug in question whereas none of the latter did

• 85% of [US medical students] who thought that accepting a small gift or lunch was inappropriate reported accepting them anyway. This may be partially explained by the fact that 93% of the students had been asked or required by a faculty member to attend a sponsored lunch
•  In one survey of internal medicine residents, 100% of those who thought interactions with industry were inappropriate accepted at least a lunch or a pen
• In a random sample of physicians in six specialties in the United States, 94% reported some relationship with industry (18). Eighty-three percent reported receiving food or beverages in the workplace; 78% received samples
• Clinicians often describe the role of samples as helping those who cannot afford medications to receive treatment... Physicians themselves report that samples influence them to prescribe drugs that differ from their preferred choices (32). Although the initial reason may be to avoid cost to the patient, most samples are of the newest and most expensive medications, which patients may not be able to afford after their samples run out. Further, the side effects of newer medications are usually less well established