You know you should always evaluate a website before using it for your research. The websites on this page are current and created by reliable places, such as the Food & Drug Administration (FDA) and the National Library of Medicine (NLM).
For example, DailyMed is the official provider of FDA medication label information (package inserts) to read or download. The National Library of Medicine (NLM) provides the website as a public service and does not accept advertisements. The drug labeling information is the most recent submitted to the FDA and currently in use for drugs available in the U.S.
You can search for complete reports on a prescription medication at one of the first two websites below; they will have information about indications, dosing, contraindications, adverse reactions, etc. The 3rd and 4th links are written for non-professionals or patients, so look for information under non-medical headings, such as Uses, Special Precautions, or Side Effects.
DailyMed (includes indications, usage, contraindications, adverse reactions, dosage, patient counseling, etc. from FDA package inserts - search by generic or brand name)
PDR.net (most information available for free from the book that's in many doctor's offices. Has prescription and some OTC drugs)
Drug Encyclopedia (easier to read, from Kaiser Permanente)
MedlinePlus: Drugs, Herbs & Supplements (these patient handouts from NLM include both prescription and over the counter drugs)
Institute for Safe Medication Practices (includes medication safety alerts, high alert medication lists, "Do Not Use" abbreviations, and current Targeted Medication Safety Best Practices for Hospitals reports.)
National Drug Code Directory (FDA listing unique drug codes for all items drug manufacturers sell or are developing for use in the U.S.)