Expected, uncommon, and the three that warrant a call.

RECOVERY / SIDE EFFECTS

PRP risk is low because the injection is your own blood. There is no donor material and no drug. Expect a two- to four-day flare, swelling, bruising and brief stiffness. A longer flare, a vasovagal reaction (feeling faint or fainting) or nerve irritation are uncommon. Fever, spreading redness or pain that climbs after day three: any one of these means you should call.

PRP has a good safety record. That is exactly why it deserves a careful page, not a soothing paragraph. A treatment called risk-free is a treatment nobody has looked at closely.

Are PRP injections safe?

The preparation is autologous — drawn from you, concentrated, and put back into you within the hour. There is no donor material. So there is no risk of catching anything and no immune rejection. There is no drug. So there is no drug side effect, nothing spreads through your body, and nothing interacts with your other medications. What is left is the risk of any injection, plus the traits of the tissue being treated.

What are the side effects of PRP injections?

The words below carry the meaning. The color is a second signal on top of them, not a stand-in for them.

Infection risk, stated precisely — and why BMAC differs

It is worth being exact here, because people often talk about the two treatments as if they carry the same risk, and they do not.

PRP has a low infection risk, and preventive antibiotics do not help it. The procedure is a blood draw from a vein and a soft-tissue injection, done under sterile conditions. Adding antibiotics to a low-risk soft-tissue shot adds side effects and pushes germs toward resistance. It adds no protection. So we do not use them.

Bone marrow aspirate concentrate carries an infection risk that is more serious, not more frequent, and that risk is reduced with antibiotics. Pooled randomized data from six trials and 860 patients puts BMAC complication rates at about 42%, against 41% for comparison injections. That is no significant difference. Effusion (fluid in the joint) was the most common event. What changes the antibiotic decision is severity, not likelihood. An infection that starts at or near bone is a longer and harder problem than one in soft tissue. The reason is the harvest. BMAC means drawing marrow out of the iliac crest (the top of the hip bone), a deeper and more invasive entry. Preventive antibiotics fit there, and we use them.

Two different procedures, two different risk profiles, two different answers on antibiotics. Anyone who covers both in one consent talk is not describing them accurately. The full comparison is here.

Who has a higher risk of PRP complications?

• Poorly controlled diabetes — raises infection risk and slows healing
• Active nicotine use — reduces blood flow to tissue that already has little
• Immunosuppression (a weakened immune system), from disease or from medication
• Anticoagulation (blood thinners), which raises bruising and needs a plan made for you
• Any active infection elsewhere in the body at the time of treatment

The risk of the alternatives, for comparison

Risk only means something next to what you would do instead. And the other options are not risk-free either.

• Repeated corticosteroid injection — cartilage loss with repeated shots into the joint, weakened and torn tendons, shrinking of the fat pad, and brief blood sugar swings that matter in diabetes.
• Long-term NSAID use — gut, kidney and heart risk that builds quietly over years.
• Surgery — anesthesia risk, infection, thromboembolism (blood clots that can travel), and a recovery measured in months. Those are not abstract. The itemized figures are in what the operation actually costs.
• Doing nothing — not neutral. You keep getting weaker and less fit, sleep gets disrupted, and moving less has metabolic costs. Each of those carries its own risk of death.

What is the downside of PRP injections?

We will not tell you PRP is risk-free, that it works for everyone, or that it regrows cartilage. The most common bad outcome is not a complication at all. It is spending money on a treatment that does not help you. That is why the candidacy assessment matters more than the injection technique.

How the preparation itself affects risk

Not all PRP is the same product. The differences have safety effects that rarely get discussed. Two variables matter most.

Leukocyte content. Leukocyte-rich preparations contain white cells that bring extra inflammatory signaling. In a tendon that may be useful, because the goal is to provoke a repair. Inside a joint it is more debated. That is because the same signaling acts on the joint lining and the cartilage. So leukocyte-poor preparations are generally preferred inside the joint. A clinic using one preparation for every site is choosing convenience over the tissue.

Volume and technique. Forcing a large volume into a dense, load-bearing tendon is not the same as placing it around the tendon. This is the cause behind most of the rare tendon injuries tied to the procedure. It is also why the Achilles in particular is treated around, not through, in most cases.

Should a steroid be mixed into PRP to reduce the flare?

Some clinics add a small dose of corticosteroid to reduce the post-injection flare. It does reduce it. It also works directly against what you are paying for. It suppresses the inflammatory chain reaction the platelets were delivered to start. The flare is uncomfortable for three days. Dulling it can cost the treatment its effect.

If the flare worries you most, that is fair. Plan around it with timing, your work schedule and pain relief that is not an anti-inflammatory. It is not a reason to undercut the injection.

What people ask about safety

Can I be allergic to it?

No — it is your own blood. That is the main safety advantage. How PRP works.

Should I take antibiotics beforehand?

For PRP, no. For BMAC, yes — different procedure, different risk. PRP compared with BMAC.

Is the flare a sign something went wrong?

No. It is expected and is the mechanism working. Escalation after day three is different. Recovery timeline. What the three days look like in order, and what is not normal.

I take a blood thinner. Can I still have this?

Often yes, with planning. It needs an individual conversation. Candidacy.

How long does pain last after a PRP injection?

Expect a flare for two to four days. That soreness is the treatment working, not a complication. Stiffness usually settles within the first week. A minority of people have a longer flare of one to two weeks, which is worth mentioning at follow-up rather than an urgent call. Pain that gets worse after day three, instead of easing, is different: call us.

What should I avoid after a PRP injection?

Skip anti-inflammatory pain relievers during the window we agree on, because they work against the healing signal the injection is meant to start. Acetaminophen and patience are usually all the flare needs. Watch for warning signs: fever or chills, redness spreading from the injection site, a hot and tense joint, any wound discharge, or pain that climbs after day three. Call us if any appear.

Is it normal to feel faint during a PRP injection?

It can happen. A vasovagal reaction, the brief lightheaded or fainting spell some people get with a blood draw or a needle, is uncommon but common enough that we plan for it. We position you during the draw and the injection to help prevent it. It is usually brief, settles on its own, and does not mean anything went wrong with the treatment.

Is it normal to have a fever after a PRP injection?

Fever is not part of a normal PRP reaction, so a temperature after treatment is a reason to call. The expected flare stays where the needle went: soreness, swelling and stiffness in the treated area, with no change in how you feel overall. A fever or chills point to something body-wide, and paired with spreading redness or a joint turning hot and tense, they are the pattern of infection, which is a same-day call rather than a question for follow-up. When to call, day by day. What is and is not normal in the first week.

Related reading

• PRP for the disc — and why discitis governs it
• PRP compared with BMAC
• PRP compared with cortisone
• Recovery timeline
• Am I a candidate?

What the first three days feel like, site by site.