Understanding Eligibility Criteria in Clinical Trials

When you read that a supplement is “clinically proven” to support joint health or that a serum “reduced wrinkles in 8 weeks,” you’re seeing the end result of a very selective process. Clinical trials don’t test products on just anyone, they rely on carefully defined eligibility criteria to decide who qualifies to participate.

In non-pharmaceutical trials, especially in the supplement, skincare, and wellness spaces, eligibility criteria quietly do the heavy lifting: ensuring valid results, preventing misleading claims, and helping brands stay compliant with marketing regulations. Let’s break down what eligibility criteria are, why they matter, and how they influence everything from recruitment to real-world evidence.

What Are Eligibility Criteria?

Eligibility criteria are the pre-set rules that determine who can or cannot participate in a clinical trial. These are typically grouped into:

• Inclusion Criteria: The characteristics a participant must have (e.g., age, lifestyle habits, specific health or skin concerns).

• Exclusion Criteria: Conditions or traits that disqualify someone (e.g., certain medications, allergies, or recent treatments).

  
  

These criteria help ensure that a clinical trial measures the product’s impact on the intended audience, reducing variability and improving the reliability of the results.

Why Eligibility Criteria Matter in Wellness Trials

In wellness-oriented trials, where the goal is often to enhance quality of life or appearance, eligibility criteria shape the very foundation of the study. Here’s why they’re essential:

1. Improves Accuracy and Relevance

A collagen powder meant for women 40+ shouldn’t be tested on 25-year-olds. Narrowing the participant pool ensures results that reflect the product’s true efficacy for the intended user.

2. Boosts Claim Credibility

Consumers are more likely to trust results when they know who participated in the trial. A claim like “Visible wrinkle reduction in 70% of women aged 45–60” has far more impact than a vague blanket statement.

3. Supports Marketing Compliance

The Federal Trade Commission (FTC) expects companies to back up clinical claims with scientifically valid, non-misleading evidence. Eligibility criteria are key to keeping your claims in line.

4. Minimizes Study Bias

By excluding participants with confounding factors, like existing supplement use or underlying conditions, brands can reduce “noise” and generate more reliable data.

How Eligibility Criteria Impact Study Recruitment

While eligibility criteria are crucial for trial quality, they also directly affect how easy (or hard) it is to recruit participants. If your criteria are too narrow, say, “women aged 40–42 with mild crow’s feet who haven’t used retinol in 6 months”, you may struggle to find enough participants, slowing down the trial.

Conversely, overly broad criteria might bring in too much variability, muddying the results.

Tip for brands: work with experienced clinical research teams or CROs (Contract Research Organizations) to strike the right balance. Use screener surveys, pre-screening interviews, or even digital recruitment platforms to streamline the process and reduce dropout rates.

Examples of Eligibility Criteria in Action

Here are some sample criteria in real-world wellness trials:

Gut Health Supplement Trial

• Inclusion: Adults aged 18–65 with self-reported mild bloating or irregularity.

• Exclusion: Recent antibiotic use, diagnosed GI disorders, current probiotic use.

Anti-Aging Skincare Trial

• Inclusion: Women aged 35–55 with visible fine lines.

• Exclusion: Recent chemical peels, laser treatments, or prescription retinoid use.

Joint Health Supplement for Pets

• Inclusion: Dogs over 7 years old with mobility issues.

• Exclusion: Dogs currently on pain medication or recovering from surgery.

These parameters ensure the product is tested on the right demographic, leading to results that brands, and consumers, can trust.

What Consumers Should Know About Eligibility Criteria in Clinical Claims

Consumers often overlook eligibility criteria when evaluating a clinical claim, but they’re a crucial part of interpreting a product’s potential.

When reading claims like “Clinically tested to improve skin elasticity,” ask:

• Who was tested? (e.g., age, gender, skin type)

• Were any users excluded? (e.g., people with sensitive skin or certain health conditions)

• Does this match your profile?

Smart shoppers understand that clinical results apply to people like those in the study, not necessarily everyone. Transparent brands that share eligibility criteria (often in a clinical summary or footnote) are signaling credibility and respect for their audience.

Best Practices for Brands Running Clinical Trials

If you're launching a clinical trial for a consumer-facing wellness product, keep these tips in mind:

• Align criteria with your target demographic. Your ideal customer should match your participant profile.

• Don’t be vague. “Healthy adults” isn’t enough, be specific about what “healthy” means.

• Publish your criteria transparently. Consider adding them to your website, product page, or white paper.

• Balance rigor with recruit-ability. Overly strict criteria may delay your study.

Eligibility Criteria Are Your Study’s Secret Superpower

Eligibility criteria aren’t just a checklist, they’re the backbone of any solid clinical study. They determine who your product is tested on, how it’s evaluated, and what you’re ethically allowed to claim in your marketing.

In a wellness market crowded with unverified claims, using well-designed eligibility criteria helps your brand stand out for the right reasons. It communicates that your clinical testing wasn’t just performative, it was precise, ethical, and built for real-world relevance.

If you’re investing in clinical trials, make sure eligibility criteria aren’t just a footnote in your protocol. They could be the difference between “clinically tested” and “clinically trusted.”

Ready to run a credible, consumer-focused clinical trial with clear eligibility criteria? Partner with Citruslabs to get results you (and your customers) can trust.