Our Methodology

Every product on rx-digestion is evaluated against the same set of criteria. We do not rank products we would not personally recommend to a family member.

Our ranking criteria, in priority order:

1. Evidence quality — are there peer-reviewed randomized controlled trials? What does the evidence actually show, and at what confidence level?
2. Strain specificity— for probiotics and synbiotics, is the exact bacterial strain identified (not just the species), and does that specific strain have clinical data behind it? Vague “probiotic blend” labeling scores lower than a named, studied strain.
3. OTC / FDA status — is the product regulated as an over-the-counter drug (with an FDA monograph), a dietary supplement, or neither? We flag the regulatory category explicitly since supplements are not FDA-approved for efficacy the way OTC drugs are.
4. Value for money — is the price justified by the evidence? If a generic or store-brand product has identical active ingredients to a name-brand product, we say so explicitly.
5. Tolerability — what are the known side effects (bloating, GI upset, die-off symptoms), how common are they, and how quickly do they resolve? We do not minimize side effects to make products look better.

We update rankings when new evidence emerges, when product formulations change, or when pricing shifts meaningfully. Every article displays its last updated date.

All content on rx-digestion is written with accuracy as the primary objective. Claims are linked to primary sources — clinical trials, FDA approval documents, and peer-reviewed reviews — not secondary coverage or marketing materials.

We are currently recruiting a board-certified gastroenterologist for our medical advisory board. Until that process is complete, articles are reviewed internally against primary literature.

What we do not do: publish claims without sourcing them, overstate the evidence for products we earn commissions from, or suppress negative findings about products in our rankings.

If you are a board-certified gastroenterologist interested in advisory board participation, contact us via the email in our footer.

We never accept payment to rank a product higher. No partner can purchase a favorable review, a top ranking, or removal of critical content from our site.

Our commission rates do not influence our rankings. When the cheapest option is also the best option, we say so. Amazon pays us a percentage of each sale, so a cheaper product earns us less, and we still rank it first when the evidence supports it.

When products have genuine downsides — like the temporary bloating or GI upset some people experience when starting a new probiotic, or the limited independent validation behind at-home gut tests — we state them plainly, even when those products are in our rankings.

If we have an affiliate relationship with a product, it is disclosed on the page where that product appears. Every article with affiliate links opens with an advertising disclosure, and the table above lists exactly what we earn.

This site exists because there is a gap in the market for evidence-based, transparent affiliate content in the gut health category. We think the approach outlined here — show your evidence, show what you earn, never let those two things mix — is the right one. If you believe we have fallen short of it, contact us.