Prescription drugs are required by the FDA (or equivalent organizations in other countries) to have a officially-approved document describing the drug, which is usually called the "label." It's also called the USPI (United States product insert) in the US, and the SmPC or SPC (summary of product characteristics) in Europe. These documents are developed by the manufacturer, and scrutinized and approved by the regulatory agency, frequently after lots of discussions and give-and-take -- the manufacturer wants to present the information in the most positive light possible, and the regulators want the information to be absolutely accurate.

If you are considering starting a new drug, you might want to look at the USPI or SPC yourself. They are loaded with technical information, and includes the following:
* description of the drug
* clinical pharmacology
* indications (uses for the drug). It must be pointed out that these are the approved indications; many drugs are used "off-label" for medical conditions that are not officially approved. For instance, metformin has been used in pre-diabetes and in PCOS, as well as for the approved indication of type 2 diabetes.
* contraindications (who should not take the drug)
* warnings
* precautions
* adverse events (side effects)
* drug abuse and dependence
* dosage and administration
* use in pregnancy, use in nursing mothers
* use in children and older patients
* how the drug is supplied
* safety information for the patient
* and also the date of the document's approval

(This listing is modified from the one at the FDA website.)

USPI documents may exist in either of two formats. The older one starts with a description of the drug, and is structured with sections following one after another after another; stuff you might be interested in (such as dosage and administration) may be buried way back in the document, and will be hard to find unless you can use your computer's "search" feature, as there's no table of contents. The newer format starts with a fairly short "Highlights of Prescribing Information" then has comprehensive "Full prescribing information" starting with a standardized table of contents -- and each section is numbered.

Where can you find a copy of the current label? It may be part of the packaging when you purchase the drug itself, but the information is also available elsewhere.

In the distant past (pre-Internet), the usual way to find labeling information was in a big book called the "PDR" (Physician's Desk Reference) that's updated annually. Most physician offices and libraries should have copies, and it's now on the Internet at http://www.pdr.net, but access is restricted to health care professionals who have appropriate code numbers to enter when registering. Anyway, the PDR in paper version is incomplete, not providing labels for many older or generic drugs, and the current labels for many drugs can be found elsewhere on-line.

The first place to look would be the manufacturer's website for the product, if they have one. Many best-selling medications (such as Lantus) can be found at websites with the product's name (such as www.lantus.com). Then it's a matter of looking around for a hyperlink to "prescribing information" or to a section named something such as "Healthcare Professionals" and clicking there.