Specialty Topics Research and Evidence: How Much Research Exists and How to Read It

Why count studies at all

How much research exists is a useful first clue. A topic with thousands of papers and many randomized trials can usually answer more questions than one with a few animal studies. But counts are not quality. A large number of papers can include reviews, lab work and opinion, and a small number can still be well designed. Use this page as a map, and then read the individual topic pages for what the studies found.

A rough PubMed snapshot

PubMed is a free database of biomedical literature that comprises more than 40 million citations. [1] The table below shows approximate counts from searches we ran on 2026-10-22, using the term in the title or abstract. The second column limits results to PubMed's randomized controlled trial publication type. The third limits them to systematic reviews or meta-analyses. [2]

Read the table with care

• Rough numbers. Search settings, spelling variants and database updates change counts. Some terms may also match papers that are not about human health. Searches without quotation marks may also match the words separately.
• A trial is not a good trial. Randomized does not mean large, long or free of bias, and PubMed's labels are applied to the paper type, not to its quality.
• Humans or animals? A count does not tell you whether the studies were in people. Cell and animal findings should not be treated as findings about people.
• Zero or few trials. BPC-157 has about 220 papers but no entries in the randomized-trial category in this search. That fits an early research area; it does not show the compound is useless or dangerous. See BPC-157.
• Many trials, narrow question. Semaglutide has many trials and is a prescription medicine; the page below covers what regulators say. See GLP-1 medicines.
• Different questions. Counts say nothing about how well a trial answered the question you care about, such as a biomarker change versus a health outcome.

Trial phases in plain terms

The FDA describes clinical trials as running from early, small Phase 1 studies to late-stage, large Phase 3 studies. [3] Phase 1 studies mainly look at how a drug interacts with the body and its side effects. Phase 2 studies involve a few hundred patients and are not large enough to show whether a drug will be beneficial. Phase 3 studies, with roughly 300 to 3,000 participants, are designed to show whether a product offers a treatment benefit to a specific population. [3] After that, an FDA review team evaluates whether the submitted studies show the drug is safe and effective for its proposed use, and the FDA also states that no drug is absolutely safe. [4]

Approved, investigational and unapproved

An approved drug has passed that review for a defined use. An investigational product is still being studied, and in limited cases patients with life-threatening conditions may reach one through a legal pathway decided with their clinician. [5] Unapproved products have not had that review. For a full comparison, see approved, investigational and unapproved peptides and safety and legal basics.

Reading health claims

NCCIH warns of misinformation, from anecdotes disguised as evidence to excessive claims by supplement makers. [6] It also notes that strong evidence behind supplement claims is often lacking. [7] Ask four questions: Who was studied? Was there a comparison group? What was measured? Who paid for or sells the product? Our pages on how we label evidence and reading early-stage research go further.