Most people feel a real change from a PRP injection somewhere between week four and week twelve. Not day three. The first week often feels worse than the day before treatment, and that soreness is part of the process rather than a sign something went wrong. Understanding that sequence is the difference between a patient who sticks with the protocol and one who quits at week two, convinced it failed.

This is a week-by-week look at what platelet-rich plasma therapy actually does inside the tissue, when patients typically notice the shift, and what changes the timeline for better or worse. The published research referenced throughout comes from the clinical studies our clinical team works from, linked at the end.

What PRP is doing while you wait

PRP treatment takes a small volume of your own blood, spins it in a centrifuge to concentrate the platelets, and places that concentrate directly into the injured tendon, ligament, or joint. Platelets carry growth factors. Once they are released into damaged tissue, they signal the local cells to start repairing.

That signal is the whole point, and it is also why PRP is slow. You are not receiving a painkiller. A cortisone shot suppresses inflammation within a couple of days, and the relief is immediate. PRP does the opposite. It provokes a controlled inflammatory response so the body restarts a repair cycle that stalled. Tissue repair runs on biology, and biology runs on its own clock.

Study reference. Castillo, Pouliot, Kim and Dragoo (Stanford University, American Journal of Sports Medicine, February 2011) measured what is actually in PRP from three commercial separation systems and found significant differences in white blood cell counts and in PDGF-ab, PDGF-bb and VEGF concentrations between them. The Cascade system produced leukocyte poor PRP with the highest platelet capture efficiency. What you are injected with is not a single standard product, and the preparation affects the biology [1].

Collagen remodelling in a tendon takes weeks. Cartilage responds even more slowly. So when patients ask when PRP starts working, the honest answer is that it starts working within hours, but you will not feel it for a month or more.

The PRP recovery timeline, week by week

Days one to three: the flare

Expect the treated area to feel sore, stiff, and swollen. Knees often feel tight and full. Tendons feel bruised. Some patients report the joint feels worse than it did before the PRP injection.

This is the inflammatory phase doing its job. Use ice sparingly if at all, because heavy anti-inflammatory measures can blunt the exact response you paid for. Most clinics ask patients to avoid ibuprofen, naproxen, and similar NSAIDs for two weeks before and after the procedure. Paracetamol is usually permitted. Confirm this with your own provider, since protocols vary.

Study reference. Dragoo and colleagues (Stanford University, American Journal of Sports Medicine, June 2012) injected leukocyte-rich and leukocyte-poor PRP into healthy rabbit patellar tendons and examined the tissue at day 5 and day 14. Leukocyte-rich PRP produced a significantly greater acute inflammatory response at day 5. By day 14 the difference had largely resolved. That is the biological basis for the short early flare patients describe, and one reason the white cell content of the preparation matters [2].

Rest the area. Walking is fine. Loading the tissue hard is not.

Days four to fourteen: settling

The flare fades. Most people return to desk work within a day or two and to light daily activity inside the first week. Pain drifts back toward the pre-treatment baseline, which can feel like nothing has happened. Nothing visible has. Underneath, the repair cascade is in its early stage, and new collagen is being laid down in a disorganised form.

Study reference. McCarrel, Minas and Fortier (Cornell University, Journal of Bone and Joint Surgery, October 2012) cultured tendon explants in PRP with different leukocyte concentrations. All PRP groups increased the type I to type III collagen ratio and reduced MMP-13 expression compared with control, which is the signature of tendon matrix being rebuilt rather than broken down. Leukocyte-reduced PRP produced the lowest inflammatory cytokine expression. The repair signal is measurable in this window even though the patient feels nothing [3].

Do not test the joint here. The tissue is biologically busy and mechanically weak.

Weeks two to six: the first real signal

This is where most patients notice the first change. It rarely arrives as a dramatic moment. It arrives as an absence. The knee does not ache on the stairs the way it used to. The elbow stops waking you at night. Morning stiffness shortens from thirty minutes to ten.

For tendon injury cases, this window is often when pain during activity drops before pain after activity does. That pattern is normal.

Controlled loading matters now. Guided physiotherapy during this phase consistently produces better outcomes than rest alone, because new collagen aligns along the lines of stress applied to it. Tissue you never load heals into a weaker, more random structure.

Weeks six to twelve: the main gains

Most of the measurable improvement in PRP results shows up here. Function improves, range of motion opens up, and patients start returning to sport or heavier work. If you are tracking your progress on a pain scale, week eight to week twelve is usually where the number moves most.

Study reference. Hechtman, Uribe, Botto-vanDemden and Kiebzak (UHZ Sports Medicine Institute, Orthopedics, 2011) followed 30 patients with 31 elbows who had epicondylitis of at least 6 months that had not responded to conservative care, including steroid injection. After a single PRP injection, mean worst pain fell from 7.2 at baseline to 4.0 at 3 months and 1.1 at final follow-up. Overall success rate was 90 per cent. Note the shape of that curve. Roughly half the total pain reduction had happened by month three, and the rest came later [4].

For PRP for knee pain and mild to moderate osteoarthritis, this is the window where patients typically report they can walk further and stand longer without the deep ache setting in.

Months three to six: consolidation

Improvement continues, more slowly. Remodelling is still active at six months. Many providers schedule the formal outcome assessment at the three-month mark and again at six, because judging PRP therapy before twelve weeks gives you an incomplete picture.

Study reference. Halpern, Chaudhury, Rodeo, Potter and colleagues (Hospital for Special Surgery, Clinical Journal of Sport Medicine, 2012) followed patients with early knee osteoarthritis (Kellgren grade 0 to II, ages 30 to 70) for a full year after a single 6 mL PRP injection, with assessments at baseline, 1 week, and 1, 3, 6 and 12 months. Pain scores dropped significantly, and function and clinical scores rose at the 6 month and 12 month marks. MRI at one year showed no worsening per compartment in at least 73 percent of cases. This is the study that most directly answers the timeline question for arthritic knees, and the answer is that the meaningful readings came at 6 and 12 months [5].

Benefits from a successful course commonly hold for six to twelve months, and sometimes longer. Some patients return annually for a maintenance injection.

Why timelines differ so much between patients

Two people with the same diagnosis can sit six weeks apart in their response. A few factors explain most of that gap.

Tissue type. Tendon and ligament injuries usually respond faster than cartilage. Blood supply and cell turnover differ, and PRP for tendon injuries often shows change by week four, while PRP for arthritis may take three months.

How long the problem has existed. A tendon that has been painful for four months generally responds faster than one painful for four years. Chronic degenerative tissue has less repair capacity to recruit. The Hechtman patients had failed at least six months of other treatment and still reached 90 percent success, so a long history is not a reason to rule the treatment out, only a reason to expect a longer wait.

Severity. Bone-on-bone arthritis is a different proposition from early cartilage wear. The Halpern data covers Kellgren grade 0 to II. PRP for joint pain in advanced disease can reduce symptoms without reversing the structural damage.

Age and general health. Platelet quality declines somewhat with age. Smoking reduces tissue perfusion and slows healing measurably. Poorly controlled diabetes does the same.

How the PRP was prepared. Castillo and Dragoo showed the composition varies by system, and both Dragoo and McCarrel showed that white cell content changes the inflammatory response. Two patients receiving "PRP" are not necessarily receiving the same thing.

Number of injections. Many protocols use a series of two or three injections spaced three to four weeks apart. Patients in a three injection series often report the clearest improvement several weeks after the final one, which pushes the full PRP healing timeline out toward month four.

What you do afterwards. Patients who complete a rehabilitation programme outperform those who rely on the injection alone. This is the single variable you control.

PRP aftercare that actually affects the outcome

The first 48 hours are about protection. After that, the job is progressive loading.

Avoid NSAIDs for roughly two weeks on either side of the procedure unless your clinician says otherwise. Skip alcohol for a few days, since it interferes with the inflammatory signalling. Keep the injection site clean and dry for 24 hours.

Return to activity in stages. Light movement and walking in week one. Gentle range of motion work from week two. Progressive strengthening from week three or four under guidance. Sport and heavy lifting usually from week six, subject to how the tissue responds.

Track something measurable. Pain out of ten during a specific activity, or the number of stairs before onset, or morning stiffness in minutes. Memory is unreliable across a twelve-week window, and patients who log data are far less likely to conclude prematurely that nothing changed.

When to conclude PRP has not worked

Twelve weeks after the final injection is a fair point to assess, and six months is the point at which the published outcome data is strongest. If there has been no measurable change in pain or function by then, the treatment has probably not produced the response you wanted in that tissue.

Speak to your provider before that point if you develop increasing pain after the first week, fever, spreading redness, or heat at the injection site. Those warrant assessment rather than patience.

Setting the right expectation before you start

PRP injection recovery is slow, non linear, and easy to misread in its early phase. Patients who understand that from day one tend to do better, partly because they rehabilitate properly instead of waiting passively for relief that was never going to arrive in week two.

Regenerative medicine works with your biology rather than overriding it. That is its advantage over repeated steroid injections, and it is also the reason it asks for patience.

Frequently asked questions

Sources

1. Castillo TN, Pouliot MA, Kim HJ, Dragoo JL. Comparison of growth factor and platelet concentration from commercial platelet-rich plasma separation systems. American Journal of Sports Medicine, February 2011.

2. Dragoo JL, Braun HJ, Durham JL, Ridley BA, Odegaard JI, Luong R, Arnoczky SP. Comparison of the acute inflammatory response of two commercial platelet-rich plasma systems in healthy rabbit tendons. American Journal of Sports Medicine, 2012;40(6):1274.

3. McCarrel TM, Minas T, Fortier LA. Optimization of leukocyte concentration in platelet-rich plasma for the treatment of tendinopathy. Journal of Bone and Joint Surgery, October 2012.

4. Hechtman KS, Uribe JW, Botto-vanDemden A, Kiebzak GM. Platelet-rich plasma injection reduces pain in patients with recalcitrant epicondylitis. Orthopedics, 2011.

5. Halpern B, Chaudhury S, Rodeo SA, Hayter C, Bogner E, Potter HG, Nguyen J. Clinical and MRI outcomes after platelet-rich plasma treatment for knee osteoarthritis. Clinical Journal of Sport Medicine, 2012.