3 Reasons Why PRP Injections Fail and How to Avoid Them

By Dr. Jeffrey Peng, MD · Published March 4, 2025 · 8 min read

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Platelet-rich plasma (PRP) injections have become one of the most promising regenerative medicine treatments for osteoarthritis, tendon injuries, and other musculoskeletal conditions. Clinical trials continue to demonstrate that PRP can outperform many conventional treatments — but not all PRP is created equal. There are three critical mistakes that can undermine the effectiveness of your PRP treatment, and each one is completely preventable.

In my practice, I frequently see patients who have tried PRP elsewhere without improvement. In nearly every case, the reason comes down to one or more of the errors outlined below. Understanding these pitfalls is the key to ensuring you achieve the best possible outcomes from your treatment.

Does Platelet Dosing Affect PRP Results?

Just like any other medication, PRP has a dose-response curve. If your provider does not administer enough platelets, you are unlikely to see meaningful clinical improvement. This lesson became widely apparent following the publication of the RESTORE trial in JAMA — one of the most highly respected medical journals in the world.

The RESTORE trial compared PRP injections to saline placebo for knee osteoarthritis and concluded that PRP did not result in significant symptom improvement at 12 months. While the study was well-designed and well-executed, it had a critical flaw: the commercial kits used (RegenLab BCT) involved only a 10 cc blood draw and achieved a platelet concentration of roughly 1.6 times baseline — yielding approximately 1 to 2 billion platelets. The true definition of platelet-rich plasma requires a concentration of at least 3 to 4 times above baseline. The product used in the RESTORE trial did not even qualify as platelet rich plasma, which explains why the results were no better than placebo.

In contrast, a large multicenter randomized controlled trial that started with a 50 cc blood draw achieved a platelet concentration of 4.3 times above whole blood — approximately 4 to 5 billion platelets per injection. This study demonstrated that high-dose PRP was superior to placebo for pain, function, and overall arthritis symptoms. Remarkably, three high-dose PRP injections significantly decreased inflammatory markers in the knee joint and slowed arthritis progression by up to 50% compared to placebo over five years of follow-up.

Other research confirms this finding. Bansal et al. (2021) reported that correct PRP dosing is critical for long-term clinical efficacy. Their protocol used a 60 cc blood draw and yielded approximately 10 billion platelets per injection. They argued that an absolute count of 10 billion platelets is crucial to produce significant chondroprotective effects and sustained symptom relief in patients with knee osteoarthritis.

The same principle applies to soft tissue injuries. A narrative review by Everts et al. (2023) found that studies using higher platelet doses consistently achieved significantly better outcomes than those using low-dose PRP for tendon injuries and tendinopathies.

How to Ensure You Get the Right PRP Dose

First, ask your provider how much blood will be drawn for your PRP treatment. The volume of the blood draw is the single best estimate of how many platelets will end up in your injection. Large joint injections such as knees and hips typically require a 50 to 60 cc blood draw to yield approximately 10 billion platelets. Smaller targets still need around 5 billion platelets, which requires roughly a 30 cc blood draw.

Second, understand that a larger blood draw alone does not guarantee adequate platelet recovery. Some single-spin centrifuge protocols recover less than 50% of available platelets. Double-spin protocols achieve significantly higher platelet recovery, which translates to higher doses and better outcomes. In my experience, most orthopedic providers use low-cost single-spin PRP kits that handle only up to 20 cc of total volume — kits that have not been shown to outperform placebo.

Third, once you have ensured you are receiving high-dose PRP processed with an optimal centrifuge protocol, it is critical that the entire sample is injected into a single target site. Splitting a 10-billion-platelet sample into five separate syringes means each injection delivers only 2 billion platelets — effectively reverting to a low-dose treatment with suboptimal results.

Why Is Ultrasound Guidance Essential for PRP Injections?

Imaging guidance is essential for PRP injections regardless of how experienced your provider may be. Even the most skilled and seasoned clinicians can miss their target when using landmark-based techniques. A comprehensive review by Daniels et al. (2018) compared the accuracy of ultrasound-guided injections versus landmark-based approaches across multiple anatomic sites. The data is striking: landmark-based injection accuracy often falls in the low to mid-60% range, while ultrasound guidance achieves accuracy rates of 87% to 100% depending on the joint.

Accurate placement becomes even more important for soft tissue conditions such as partial tendon tears. A randomized controlled trial by de Castro et al. (2023) evaluated ultrasound-guided tendon debridement (barbotage) followed by either PRP or saline placebo for partial supraspinatus tendon tears. In the PRP group, 87% of patients experienced a reduction in tear size by six months, and 79% achieved complete healing. The saline group showed only 32% reduction in tear size with 21% achieving full healing.

These outcomes are simply not achievable with landmark-based injection techniques. If your provider does not use imaging guidance for PRP injections, consider finding a sports medicine specialist who has the technical skills and equipment to ensure correct placement.

Should You Stop NSAIDs Before PRP Injections?

The third critical mistake is taking nonsteroidal anti-inflammatory drugs (NSAIDs) around the time of your PRP treatment. Common NSAIDs include aspirin, ibuprofen, naproxen, diclofenac, and indomethacin. Platelets release growth factors that are essential for the healing process, and NSAIDs directly inhibit platelet function — potentially reducing the effectiveness of the growth factors that PRP therapy relies on to initiate tissue repair.

A prospective study by Jayaram et al. (2019) demonstrated that daily use of low-dose aspirin significantly reduced the expression of vascular endothelial growth factor (VEGF), platelet-derived growth factor (PDGF), and TGF-beta-1 in platelet-rich plasma. This means that taking NSAIDs before your PRP procedure can impair the ability of your platelets to initiate the cascade of growth factor release necessary for a proper healing response.

It is also important to understand that while chronic inflammation can be harmful, acute inflammation is a necessary part of the body's natural healing process. The initial inflammatory response following a PRP injection signals the body to begin repairing injured tissue. By suppressing this response, NSAIDs can directly interfere with the mechanism that makes PRP effective.

Animal research supports this concern. Sok et al. (2022) found that rats given NSAIDs after orthobiologic injections had significantly worse osteoarthritis outcomes compared to those that did not receive NSAIDs. The use of anti-inflammatory medications after injection inhibited growth factor release and resulted in measurably worse cartilage preservation.

While some evidence suggests that selective COX-2 inhibitors such as meloxicam and celecoxib may not significantly impair healing, the data remains inconclusive. In my opinion, if you are going to invest in PRP, it is best to stop all NSAIDs to minimize any disruption to the healing process.

NSAID Recommendations Around PRP Treatment

Stop taking NSAIDs at least one week before your PRP injection. Continue to avoid them for at least two weeks after treatment, and ideally up to six weeks. The longer you can hold off on NSAIDs following a biologic treatment, the better your outcomes are likely to be. Acetaminophen (Tylenol) remains a safe alternative for pain management during this period.

The Bottom Line

The three most common mistakes that undermine PRP treatment outcomes are insufficient platelet dosing, failure to use imaging guidance for injection accuracy, and taking NSAID medications around the time of treatment. Each of these errors is entirely preventable. By asking the right questions and choosing a provider who understands these principles, you can significantly improve your chances of a successful outcome. If you are considering PRP therapy or have had an unsuccessful experience in the past, I encourage you to schedule a consultation to discuss whether a properly executed PRP protocol may be right for you.

References

1. Bennell KL, Paterson KL, Metcalf BR, et al. Effect of Intra-articular Platelet-Rich Plasma vs Placebo Injection on Pain and Medial Tibial Cartilage Volume in Patients With Knee Osteoarthritis: The RESTORE Randomized Clinical Trial. JAMA. 2021;326(20):2021-2030. doi:10.1001/jama.2021.19415

2. Chu J, Duan W, Yu Z, et al. Intra-articular injections of platelet-rich plasma decrease pain and improve functional outcomes than sham saline in patients with knee osteoarthritis. Knee Surg Sports Traumatol Arthrosc. 2022;30(12):4063-4071. doi:10.1007/s00167-022-06887-7

3. Bansal H, Leon J, Pont JL, et al. Platelet-rich plasma (PRP) in osteoarthritis (OA) knee: Correct dose critical for long term clinical efficacy. Sci Rep. 2021;11(1):3971. doi:10.1038/s41598-021-83025-2

4. Everts PA, Lana JF, Onishi K, et al. Angiogenesis and Tissue Repair Depend on Platelet Dosing and Bioformulation Strategies Following Orthobiological Platelet-Rich Plasma Procedures: A Narrative Review. Biomedicines. 2023;11(7):1922. doi:10.3390/biomedicines11071922

5. Daniels EW, Cole D, Jacobs B, Phillips SF. Existing Evidence on Ultrasound-Guided Injections in Sports Medicine. Orthop J Sports Med. 2018;6(2):2325967118756576. doi:10.1177/2325967118756576

6. de Castro RLB, Antonio BP, Giovannetti GA, Annichino-Bizzacchi JM. Total Healing of a Partial Rupture of the Supraspinatus Tendon Using Barbotage Technique Associated with Platelet-Rich Plasma: A Randomized, Controlled, and Double-Blind Clinical Trial. Biomedicines. 2023;11(7):1849. doi:10.3390/biomedicines11071849

7. Jayaram P, Yeh P, Patel SJ, et al. Effects of Aspirin on Growth Factor Release From Freshly Isolated Leukocyte-Rich Platelet-Rich Plasma in Healthy Men: A Prospective Fixed-Sequence Controlled Laboratory Study. Am J Sports Med. 2019;47(5):1223-1229. doi:10.1177/0363546519827294

8. Sok D, Raval S, McKinney J, et al. NSAIDs Reduce Therapeutic Efficacy of Mesenchymal Stromal Cell Therapy in a Rodent Model of Posttraumatic Osteoarthritis. Am J Sports Med. 2022;50(5):1389-1398. doi:10.1177/03635465221083610

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. The information presented reflects the opinion of Dr. Jeffrey Peng and does not represent the views of his employers or affiliated hospital systems.