Stem Cells vs. PRP: What the Evidence Actually Shows

Evidence reviewed through: July 2026

Start Here: An Honest Summary

Regenerative injections are among the most oversold treatments in musculoskeletal medicine. That does not mean they do nothing — the evidence for PRP in particular has strengthened considerably in the last two years. It means the gap between what is advertised and what has been demonstrated remains unusually wide.

The state of play, stated plainly:

• PRP for knee arthritis is now a defensible, guideline-supported option for mild-to-moderate disease, with a favourable safety profile and effects that outlast a cortisone injection.
• Cell therapy is more promising than proven. It helps symptoms in many trials, but the effect over and above placebo is modest, the trials are small, and the evidence quality is mostly low.
• Neither has convincingly regrown cartilage in a human trial. If a provider tells you otherwise, ask which trial.
• Both are safe in the sense that serious complications are rare — but "safe" is not "effective," and the two are frequently conflated in sales conversations.

If you take one thing from this article: the honest question is not "which one rebuilds my joint?" but "which one gives me the best chance of feeling meaningfully better, at what cost, with what certainty?"

What is PRP?

Platelet-Rich Plasma (PRP) uses a concentrate of your own blood platelets.

How PRP is Prepared

1. Blood draw — a small volume of blood is drawn from your arm, as in a routine blood test
2. Centrifugation — the blood is spun to separate its components
3. Concentration — the platelet-rich fraction is separated off
4. Injection — the concentrate is injected into the target area, usually under ultrasound guidance

What Platelets Actually Do

Platelets are not only clotting agents. Their alpha granules store growth factors in inactive form — principally transforming growth factor beta (TGF-β), vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF) and epidermal growth factor (EGF) — alongside adhesion molecules such as vitronectin. On activation, platelets release bioactive proteins that recruit macrophages, mesenchymal stem cells and osteoblasts, supporting clearance of damaged tissue and the healing response (Sampson et al., 2008).

A note on a common claim. Marketing material frequently states that platelets contain "over 1,500 proteins." We have not been able to trace that figure to a primary source. The named growth factors above are what the published reviews actually document.

PRP is not one product — and this matters more than almost anything else

This is the most practically useful thing on this page.

PRP preparations differ enormously between clinics: in platelet concentration, in whether white blood cells are included (leukocyte-rich vs leukocyte-poor), in activation method, and in the number of injections given. Recent work shows these differences change outcomes:

• Platelet dose follows an inverted-U curve, not "more is better." A meta-analysis of 32 trials classified injections by total deliverable platelets. All doses beat hyaluronic acid, but the moderate dose (5–10 billion platelets) produced a large effect size, while both low (1–5 billion) and high (>10 billion) produced only moderate effects. The authors concluded that counts between 1 and 10 billion may reduce pain more than counts above 10 billion (Hooper et al., 2026).
• Leukocyte content drives the side effects. In a meta-analysis of 32 RCTs, leukocyte-rich PRP caused significantly more mild pain and swelling than hyaluronic acid — but leukocyte-poor PRP showed no significant difference from HA (p = .51) (Nakagawa et al., 2026).

"PRP" on a price list tells you very little about what you are receiving. This heterogeneity is the most credible explanation for why trials have disagreed for a decade.

What Are Mesenchymal Stromal Cells?

MSCs (usually marketed as "stem cells") are multipotent cells sourced from bone marrow, adipose tissue, or perinatal tissue such as umbilical cord.

Their proposed mechanisms are:

• Paracrine signalling — secreting bioactive molecules that alter the joint environment
• Immunomodulation — damping inflammatory activity within the joint
• Differentiation — potential to form cartilage-like tissue

The third mechanism is the one most heavily promoted and the least demonstrated in humans. The evidence increasingly points the other way: where cell therapy does something measurable to joint tissue, it appears to act on inflammation rather than on cartilage. In a double-blind trial of umbilical cord MSCs, MRI showed no significant change in joint structures except the synovium — the joint lining — where inflammation improved significantly (Tong et al., 2025).

That is a meaningful mechanism. It is simply not the mechanism most patients are sold.

The Mechanistic Difference

Practical Comparison

Figures describe published trial evidence, not outcomes at any particular clinic. Pricing is market information, not a research finding.

What the Research Actually Says

This section is written for readers who want the evidence itself. Every study named is cited in full at the end.

PRP for knee osteoarthritis: the evidence has strengthened

European society consensus now supports it. The ESSKA-ORBIT consensus on blood-derived orthobiologics issued three grade-A recommendations — its highest evidence tier: that there is sufficient preclinical and clinical evidence to support PRP use in knee OA; that PRP is effective in mild-to-moderate disease (KL ≤ 3); and that PRP provides a longer-lasting effect than corticosteroid injection, with a safer profile and fewer complications (this last with very strong agreement, mean 8.7/9). The panel positioned PRP as a valid treatment option and a possible first-line injectable for KL 1–3 knee OA. Note the panel's own candour: only 9 of 28 statements had high-level scientific support (Laver et al., 2024).

Pooled double-blind trials favour PRP over hyaluronic acid. A 2025 meta-analysis restricted to 15 double-blinded RCTs (1,632 patients, KL I–III) found PRP significantly better than HA at 12 months on WOMAC pain (MD −1.14) and WOMAC total (MD −7.33) — both crossing the minimal clinically important difference — and on VAS (MD −0.35) (Li et al., 2025). Restricting to double-blind trials matters, because it addresses the most common objection to the older positive literature.

An umbrella review agrees. Pooling across existing meta-analyses using AMSTAR 2 quality appraisal, PRP was superior to both hyaluronic acid and placebo for pain and function, with clinically relevant improvements especially in mild-to-moderate disease and a favourable safety profile (Ventura-García et al., 2026).

But the single most rigorous placebo-controlled trial remains negative, and it should not be dismissed. The RESTORE trial randomised 288 people with mild-to-moderate knee OA to three weekly injections of leukocyte-poor PRP or saline placebo, with participants, injectors and assessors blinded. At 12 months, the difference in knee pain was −0.4 points on an 11-point scale (95% CI −0.9 to 0.2; P = .17), far below the 1.8-point threshold set as clinically meaningful. Medial tibial cartilage volume differed by −0.2% (P = .81). Of 31 prespecified secondary outcomes, 29 showed no significant difference. The authors concluded the findings "do not support use of PRP for the management of knee OA" (Bennell et al., 2021).

Nor is the advantage over hyaluronic acid uniform across individual trials. A randomised controlled trial comparing PRP directly with viscosupplementation found no significant difference between them at any timepoint, and more post-injection swelling and pain in the PRP group (Filardo et al., 2015). One trial does not overturn a pooled analysis, but it belongs in the picture: this comparison is more consistent in meta-analysis than in any single study.

How to hold all of this. The most coherent reading of the current literature: PRP probably does outperform hyaluronic acid and clearly outlasts corticosteroid, while whether it beats a genuinely inert placebo remains unsettled. Formulation differences — platelet dose and leukocyte content — plausibly account for much of the inconsistency, which is why the dose and composition findings above matter so much.

MSC therapy for knee osteoarthritis: promising, not proven

The most current synthesis is measured. A 2026 systematic review and meta-analysis of 28 RCTs found MSC therapies significantly improved pain (ΔVAS MD −1.67, p = 0.007; KOOS pain MD 15.37, p = 0.03) and several function domains (KOOS activities of daily living, sports, symptoms). But WOMAC, KOOS quality of life and the Lequesne Index showed no significant differences, and MRI-based WORMS scores were non-significant — "indicating no consistent structural benefit." The authors' conclusion is the clearest one-line summary available: current evidence supports a "primarily symptom-modifying rather than structure-modifying role" (Awad et al., 2026).

Society consensus places it second-line. The 2025 ESSKA-ORBIT consensus on cell-based therapy assembled 77 experts across 22 European countries. It found consistent clinical benefits in pain and function up to 12 months, supporting use in KL 1–3, with "some benefits, though inferior, in selected KL Grade 4." Because of limited high-quality studies and a lack of clear superiority over other injectables, the panel concluded cell therapy "should be considered as a second-line treatment option," after other non-operative treatment fails. Critically, of 27 statements, only 5 reached recommendation level A or B — 22 were rated C or D (low-level evidence or expert opinion) (de Girolamo et al., 2025).

Against inert placebo, the pooled signal is weak. A meta-analysis of 13 Level-1 RCTs found no significant difference between MSC injection and placebo for VAS pain or WOMAC pain, function or stiffness. Against hyaluronic acid, MSCs reached statistical significance on several scores — but the smallest treatment effects did not exceed the minimum clinically important difference, and the proportion of patients crossing that threshold did not differ (Dai et al., 2021).

And here is the finding that explains the most. A 2025 meta-analysis set out to quantify how much of the improvement after MSC injection is attributable to contextual effects — placebo response, expectation, the ritual of a high-cost procedure. Across 8 placebo-controlled RCTs (467 patients), contextual factors accounted for approximately 63% of pain reduction and 61% of functional improvement at 6 months, and about 50% of pain relief and 66% of functional gains at 12 months, with very low heterogeneity. The authors concluded that "the majority of symptomatic improvement following intra-articular MSC injections is attributable to contextual (placebo) effects, whereas the MSCs themselves confer only a modest incremental benefit." Certainty of evidence was rated low by GRADE (Yin et al., 2025).

This does not mean patients are imagining their improvement — contextual benefit is real benefit, and people genuinely feel better. It means that when someone tells you "I had stem cells and my knee is much better," roughly half to two-thirds of that improvement would likely have occurred with a saline injection delivered with equal care and conviction.

Dose and source appear to matter. A network meta-analysis of 11 RCTs (602 participants) found moderate-dose adipose-derived MSCs (20–50 × 10⁶ cells) produced the greatest long-term pain and function improvement with balanced safety, while high-dose adipose MSCs gave better short-term analgesia but more adverse events (Xie et al., 2026). A separate network meta-analysis of 16 RCTs (622 patients) found repeated injections outperformed single injections at 6 and 12 months — but also carried a higher incidence of adverse events (Deng et al., 2025).

Umbilical cord MSCs specifically — the source many international clinics use — have the thinnest evidence of all. A small randomised phase I/II trial found repeated UC-MSC dosing outperformed hyaluronic acid at 12 months on WOMAC pain (1.1 vs 4.3; P = .04) and VAS (2.4 vs 22.1; P = .03), with no differences in MRI scores (Matas et al., 2019; n = 26). A more recent double-blind, placebo- and HA-controlled trial (55 randomised) found UC-MSCs produced greater VAS and EQ-5D improvement than placebo and HA, but the differences were not statistically significant in the overall group. Significant benefits appeared in the subgroup with synovitis and moderate-to-severe pain, and MRI showed change only in the synovium. The authors called for phase III trials (Tong et al., 2025).

A subgroup finding in a 55-patient trial is a hypothesis, not a result. It is worth knowing, and it is worth not overreading.

Does either regrow cartilage?

Direct answer: no human trial has convincingly demonstrated cartilage regeneration from either therapy.

• RESTORE measured cartilage volume by MRI as a co-primary outcome and found no difference from saline (Bennell et al., 2021).
• The 28-RCT meta-analysis found WORMS structural scores non-significant (Awad et al., 2026).
• The umbilical-cord phase I/II trial found no MRI differences (Matas et al., 2019); the later double-blind trial found change only in the synovium (Tong et al., 2025).
• One earlier meta-analysis found increased cartilage volume but no change in WORMS (Ma et al., 2020).
• A 60-month placebo-controlled trial did report structural improvement on MRI at 12 months (P < .02) (Jafar et al., 2026).

The honest summary: a weak, inconsistent structural signal from small studies, with the largest and best-controlled trials negative. Nothing in the verified literature supports the claim, common in marketing, that either therapy forms new cartilage-like tissue and restores joint architecture.

How long does it last?

PRP outlasts cortisone. That is one of the ESSKA-ORBIT panel's grade-A conclusions, held with very strong agreement (Laver et al., 2024). Most PRP trials follow patients to 12 months, so claims beyond that are extrapolation.

For cell therapy, benefit is consistently demonstrated to about 12 months (de Girolamo et al., 2025). Beyond that the data thins sharply. A double-blind, placebo-controlled trial in stage III knee OA followed participants to 60 months: clinical scores improved significantly at 6, 12, 24 and 36 months, then "declined steadily after 36 months, with scores nearing baseline at 60 months." The authors describe benefit "for up to 3 years" — from 29 completers, with blinding maintained only to 12 months (Jafar et al., 2026). A separate phase I/II trial reported maintained improvement at 4 years in 30 patients (Lamo-Espinosa et al., 2018), and an uncontrolled 5-year series of 11 patients given a single high-dose adipose MSC injection reported pain and function significantly improved from 6 months through to 5 years, with no treatment-related adverse events across the full period (Kim et al., 2022).

Those results point in different directions, and the difference is informative. The uncontrolled series shows benefit sustained at five years; the placebo-controlled trial shows it fading to baseline by five years. Since roughly half to two-thirds of symptomatic improvement after MSC injection is attributable to context rather than the cells (Yin et al., 2025), a study without a comparison group would show sustained improvement either way. Controlled follow-up is what settles a durability claim.

The most-cited long-term result in stem-cell marketing — Davatchi's 5-year follow-up — is a three-patient case series. Those patients improved at 6 months, then "started gradually to deteriorate," remaining better than baseline at 5 years. The authors' own conclusion is a call for further study, and they noted their transplanted knees "were all in a rather advanced stage of OA," suggesting "earlier transplantation may give better results" (Davatchi et al., 2016). Three patients cannot establish durability.

Specific durability figures — "6–18 months" for PRP, "2–5 years or longer" for stem cells — circulate widely in clinic marketing. No trial we could verify measures durability that way. If you are quoted a figure like that, ask which study produced it and how long that study actually followed its patients.

The "advanced degeneration" question — where the common framing is backwards

A widespread commercial framing holds that PRP suits early arthritis while stem cells are the answer for bone-on-bone disease. Both formal European consensuses and the available cohort data point the other way.

• The ESSKA-ORBIT cell-therapy consensus supports use in KL 1–3, with benefits "though inferior, in selected KL Grade 4" (de Girolamo et al., 2025).
• The ESSKA-ORBIT PRP consensus establishes effectiveness for KL ≤ 3 (Laver et al., 2024), and the ESSKA-ICRS consensus rated PRP inappropriate in KL IV — and inappropriate as a first treatment before conservative measures, while appropriate after those fail (Kon et al., 2024).
• A propensity-score-matched cohort compared adipose stem cell therapy in moderate (KL 2–3) versus severe (KL 4) knee OA, 98 patients per matched group. Both improved, but KL 2/3 patients showed greater gains across KOOS Total, activities of daily living, sport, quality of life and VAS pain. The authors concluded "preserved joint structure benefits therapeutic efficacy" and that findings indicate "limited regenerative potential in end-stage disease" (Nakano et al., 2026).

Taken together: severe, bone-on-bone disease is where both treatments weaken, not where cell therapy comes into its own.

The distinction worth holding: PRP is reasonable as the first injection you try, but not as the first thing you try. Exercise therapy and weight management come first.

Tendon problems — the answer depends on which tendon

Do not generalise across tendons. The evidence is genuinely site-specific.

• Achilles tendinopathy: no benefit over placebo. A 2026 meta-analysis of 4 RCTs (337 patients) found no significant difference between PRP and placebo in VISA-A scores at 3 or 6 months, no difference in VAS, and no difference in tendon thickness or vascularity on imaging (Assi et al., 2026). This confirms and strengthens the older finding that the single available Achilles RCT was null (Di Matteo et al., 2015).
• Rotator cuff tendinopathy: modest but durable benefit over cortisone. A Level-I meta-analysis of 10 RCTs (591 patients) found no difference at 3–6 weeks or 3 months, but at 6 months PRP improved ASES (+10.8), Constant-Murley (+10.7) and pain (VAS −0.8), with fewer adverse events than corticosteroid (RR 0.66). The authors describe the benefit as "statistically significant, although clinically modest" (Yuwarungsikul et al., 2026).
• Patellar tendinopathy: favourable, on thin evidence. A systematic review found PRP superior to shockwave therapy and dry needling, but included only 3 RCTs across both patellar and Achilles sites and identified "the paucity of high-level literature" as its main finding, positioning PRP for recalcitrant cases (Di Matteo et al., 2015).

On cell therapy for tendon, the one published head-to-head comparison is instructive. Twenty patients aged 18–48 with chronic patellar tendinopathy received either bone-marrow MSCs or leukocyte-poor PRP. Both improved, with no significant difference between them on pain or VISA-P. The MSC group showed significantly greater improvement in tendon structure on ultrasound and MRI. Both were safe (Rodas et al., 2021).

Age is sometimes offered as a way to choose between the two — PRP for younger patients, cells for older ones. We found no evidence supporting that split. The only head-to-head trial enrolled patients aged 18–48 and found no symptomatic difference between the treatments; the comparison has not been tested in older adults at all.

Combining the two

A meta-analysis of six controlled trials (493 patients) found MSC+PRP produced no significant VAS benefit at 3 months, but significant benefit at 6 and 12 months versus control, versus hyaluronic acid, and versus PRP alone. WOMAC favoured the combination at 3 and 6 months, but not at 12 months versus control; KOOS showed no significant difference at 12 months. Adverse events were no more frequent than with MSCs alone (Zhao et al., 2022). Separately, the PRP umbrella review found PRP combined with hyaluronic acid produced better functional recovery than PRP alone (Ventura-García et al., 2026).

A real signal on pain, inconsistent on function, from a modest evidence base. That justifies further study, not a claim of established optimum.

Safety

Both therapies have a reassuring but not spotless record. Precision matters here.

• PRP: Across 32 RCTs (1,268 PRP-treated knees), adverse events occurred in 18.7% of cases, most commonly mild pain and swelling (10.6%). Leukocyte-rich PRP caused significantly more of this than hyaluronic acid; leukocyte-poor PRP did not differ from HA. No severe adverse events were reported in any group (Nakagawa et al., 2026).
• Cell therapy: The 28-RCT meta-analysis found significantly higher rates of injection-site pain (RR 2.04), joint swelling (RR 3.39) and other adverse events (RR 1.26). Serious complications such as infection were uncommon and non-significant. The authors describe the profile as "generally manageable but non-negligible" (Awad et al., 2026). Repeated dosing raises adverse event rates further (Deng et al., 2025).
• Harvest matters. A Level-I meta-analysis found no serious adverse events attributable to adipose MSCs or stromal vascular fraction, but observed complications from the liposuction harvest itself, concluding this limits their ability to displace simpler treatments (Han et al., 2025).

Precise serious-complication rates — figures like "<0.1%" — are quoted routinely for both therapies. We could not trace that number to any published source. What the trials actually support is stated above: no severe adverse events were reported in the pooled PRP safety analysis, and serious complications in the cell-therapy trials were uncommon and not statistically increased. Those are the defensible statements. A decimal percentage with no denominator behind it is not.

The Information Problem

This deserves its own section, because it affects how you will encounter every other claim on this page.

A 2026 systematic review did something unusual: it reviewed the RCT evidence for injectable orthobiologics and, in parallel, reviewed how news media portrayed them. Of 14 placebo-controlled RCTs, 8 showed significant pain improvement and 10 showed functional improvement, though "heterogeneity and risk of bias were frequent."

The media picture looked different. Across 124 news articles:

• 79.0% highlighted therapeutic benefits
• only 29.8% mentioned any drawback
• 37.1% used the term "stem cell" without specifying what product was actually involved
• 35.5% mentioned commercial entities, with no corresponding disclosures
• 66.1% were favourable in tone

The authors concluded that this disconnect "may encourage unrealistic expectations and premature adoption of these therapies" (Zhang et al., 2026).

We include this because we are also a commercial entity writing about treatments we offer. You should apply the same scepticism to this page that you would to any other. The difference we are aiming for is that everything above is traceable to a named, verifiable study — and where the evidence is weak, we have said so.

If You Are Considering Treatment Abroad

Many cell therapies are not licensed for osteoarthritis in the patient's home country, so treatment often involves travel. That is a legitimate route, and it is also one where patients are most exposed.

A review of international stem cell tourism notes that most clinics offering these therapies are based in low- and middle-income countries, that patients risk receiving unproven treatment, and that reported complications include infection, rejection and tumorigenesis. It also found that such clinics do not generally provide even basic travel health information (Lyons et al., 2022).

None of that describes every provider. It does describe a real pattern, and the practical response is to ask specific questions:

• Under what regulatory framework was the cell product manufactured, and to what standard?
• Is the product characterised — cell type, dose, viability — and will I see those figures?
• What is the plan if a complication develops after I fly home?
• Is there published trial evidence for this product, or only for the general category?

A provider comfortable answering these is giving you better information than one who redirects to testimonials.

What Clinical Guidelines Say

Guidelines matter because they weigh the whole evidence base rather than a favourable subset.

As RESTORE's authors noted, most clinical guidelines have not recommended PRP for knee OA, even as its use increases (Bennell et al., 2021). The European consensus documents above represent a more permissive recent position, and the divergence between them is itself informative.

Cost and Value

What the economic evidence shows

A Markov decision analysis modelled PRP for a 55-year-old with KL II–III knee OA and found it not cost-effective, identifying the reason precisely: "the primary factor preventing PRP from being cost-effective is not the price per injection but rather a lack of established clinical efficacy" (Rajan et al., 2020). That analysis predates the stronger 2024–2026 efficacy evidence, which is worth weighing — but no updated model has been published.

For cell therapy, one analysis found allogeneic umbilical cord blood–derived MSCs cost-effective compared with microfracture in South Korea, at an ICER of $16,812 per QALY (Suh et al., 2023). Note the comparator is a surgical cartilage procedure, not PRP, and the analysis is specific to one health system.

There is no published head-to-head cost-effectiveness comparison of PRP versus MSC therapy. We searched specifically for one and found none. Any cost comparison between the two is therefore assembled from separate analyses with different comparators, time horizons and health systems — not measured directly.

How to think about cost without a model

Because durability beyond 12 months is uncertain, any multi-year projection rests on assumptions rather than data. Useful questions:

• What is the total programme cost, including follow-up and any repeat injections?
• Would I still consider this worthwhile if the benefit lasted 12 months? (That is what is consistently demonstrated.)
• How does this compare with the cost of exercise therapy and weight management, which have stronger evidence?
• If roughly half the benefit is contextual, what am I actually paying a premium for?

That last question is uncomfortable, and it is the right one to ask.

Questions to Discuss With a Clinician

This article cannot tell you which treatment is right for you, and any source that claims to — including a flowchart — is overstating what the evidence supports.

About your situation:

• What is my Kellgren-Lawrence grade? (KL 1–3 is where both treatments have support; KL 4 is where both weaken.)
• Have I completed a proper course of exercise therapy, weight management and appropriate analgesia?
• Is there active synovitis — inflammation of the joint lining? Recent evidence suggests that may be where cell therapy does most of its work.

About the treatment:

• For PRP: leukocyte-rich or leukocyte-poor? What platelet dose? How many injections?
• For cell therapy: what source, is it lab-expanded, and under what regulatory framework was it made?
• What outcome, at what timepoint, would count as success — and what happens if that is not reached?

About the evidence:

• What does the provider consider the strongest trial supporting this treatment, and what does the strongest trial against it show?

A provider who can answer that last question comfortably is giving you better information than one who cannot.

Where the Evidence Is Genuinely Thin

Stated plainly:

• No head-to-head RCT of PRP versus MSC therapy for knee osteoarthritis exists. We searched specifically for this. Every comparison between them, including this article's, is indirect.
• No head-to-head cost-effectiveness comparison exists either.
• Cell therapy trials are small — typically 20 to 60 patients. The 60-month study had 29 completers; the largest UC-MSC trial randomised 55.
• Evidence quality is mostly low. The ESSKA-ORBIT cell-therapy panel graded 22 of its 27 statements C or D. The contextual-effects meta-analysis was rated low certainty by GRADE.
• Follow-up is short. Benefit is consistently demonstrated only to 12 months.
• Product heterogeneity is severe. "PRP" and "stem cells" each describe families of quite different products.
• Structural outcomes are the weakest area of all — the claim most often made commercially has the least support.

None of this means these treatments do not work. It means the honest answer to "will this work for me?" is we cannot reliably predict it — and you are entitled to hear that before deciding.

Take the Next Step

Not Sure Which Is Right for You?

Begin the Sterling Wellness Assessment — a short questionnaire covering your condition, history and goals, to help structure a conversation with a clinician.

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• PRP discussion: review your imaging, discuss what the evidence does and does not show, determine candidacy
• Cell therapy discussion: evaluation, what the treatment involves, regulatory and manufacturing questions, programme details

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We would rather tell you the evidence is uncertain than sell you certainty that does not exist. Our commitment is transparent communication about what is known, what is not, and what remains under investigation — through Sterling-certified partner clinics.