"What's the latest evidence on PCSK9 inhibitors - are they worth the cost?"
"Can magnesium prevent migraines? If so, what route of administration is best?"
"My patient is losing hair after starting duloxetine - is this common, and is it reversible?"
Where you look for answers depends on the nature of your clinical or research question. Some questions are background questions, addressing who, what, when, where, how or why. For instance, "what are the contraindications of drug x?" These can often be answered by tertiary sources.
Other questions can be thought of as foreground questions. These relate to a specific patient or situation, and their answers will inform your clinical decision making. Foreground questions may be framed in PICO format:
P: patient, population, problem
I: intervention or issue affecting patient/problem
Often, due to the specificity of foreground questions, you'll need to search the primary literature for an answer. However, secondary sources are often a good first step in understanding the scope of the literature for a particular condition.
Major types of secondary sources include evidence summaries, systematic reviews, and guidelines.