New Study Says PRP Doesn’t Work — Why the Dosing Problem Explains the Results
- Aug 9
- 3 min read
Updated: Aug 24
By Dr. Jeffrey Peng, MD · Updated August 2026
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A recent study followed patients for five years after PRP injections for early knee osteoarthritis and found that outcomes were no better than standardized conservative management. Headlines quickly framed this as evidence that PRP does not work. That conclusion is incorrect. This study is another clear example of why platelet dosing is the central variable that determines whether PRP helps or fails.
What the Study Found
Researchers followed more than 100 people with early knee osteoarthritis who received PRP and compared them to patients managed with education, exercise, weight management, oral anti-inflammatories, and hyaluronic acid injections. At five years both groups had worsened — pain scores rose and function scores declined. On the surface this looks like a negative result for PRP.
The Critical Flaw: Extremely Low Platelet Dose
The PRP used in the study contained only about 2.4 billion platelets per injection. That is an extremely low dose. Over the last several years, multiple clinical trials and systematic reviews have shown that platelet dose is one of the strongest predictors of outcome in knee osteoarthritis. Several analyses indicate that a minimum of roughly 5 billion platelets is needed for a meaningful clinical effect, and higher-quality data support targeting closer to 10 billion platelets for large joints.
We have seen this exact pattern before. The RESTORE trial and the PEAK trial both used low-dose PRP in the approximately 2-billion-platelet range and found no benefit over saline placebo. When the absolute number of platelets delivered is that low, results are consistently poor. Underdosed PRP does not prove that the therapy fails; it proves that dose matters.
What This Looks Like in Everyday Practice
Unfortunately, many clinics still offer PRP without attention to these details. A common approach is drawing only 10–20 cc of blood, which typically yields around 2 billion platelets — essentially the same underdosed preparation used in the negative trials. This is one of the most frequent issues I see when patients come for a second opinion after a failed PRP injection elsewhere. The first question I ask is how much blood was drawn; the answer is almost always a small volume.
Even when a larger volume is drawn (for example 60 cc), the preparation system still matters. Many commercial systems recover only 40–70% of available platelets. Higher-recovery systems can achieve rates above 90%. That difference can nearly double the number of platelets delivered from the same blood draw. More platelets, when delivered with proper technique, correlate with better outcomes.
Real-World Results with Adequate Dosing
In my practice, patients with even advanced (grade-four) osteoarthritis who receive properly dosed PRP on a periodic basis — often every six to twelve months — are frequently able to stay active, continue sports such as tennis or pickleball, and maintain the quality of life they want. The difference between those results and the negative trials is not mysterious; it is largely a function of platelet dose and preparation quality.
Bottom Line
A study that uses an extremely low platelet dose and finds no benefit does not mean PRP “doesn’t work.” It means the preparation was inadequate. Platelet number and kit recovery are not minor technical details — they are central to whether patients improve. For a deeper discussion of the dose-response data, see my posts on platelet dosing for knee arthritis and how many platelets you need.
If you are considering PRP or have had a previous injection that did not help, schedule a consultation to discuss whether a properly dosed approach is appropriate for your situation.
References
1. Five-year PRP vs conservative management study: PubMed 41926442.
2. Minimum effective dose data: PubMed 38513880.
3. Ideal dosing target: PubMed 39331322.
4. RESTORE trial: PubMed 34812863.
5. PEAK trial: PubMed 35638203.
Medical Disclaimer: This content is for educational purposes only and does not substitute for the medical advice of a physician. Always consult your healthcare provider before beginning any new treatment program.
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