PRP for Hair Loss: What the Studies Actually Show (Including the Negative Trials)

Platelet-rich plasma, or PRP, has been proposed as an option for androgenetic alopecia since the early 2010s. The procedure involves drawing a patient's own blood, spinning it to concentrate the platelets, and injecting the resulting plasma into the scalp. Proponents suggest that growth factors released by platelets might stimulate hair follicles. The published literature, however, is mixed: some small trials report increases in hair density, while others—including double-blind, placebo-controlled studies—found no significant benefit.

This page walks through what PRP is, how it is proposed to work, the positive trials, the null and negative trials, what meta-analyses conclude, the role of PRP after a hair transplant, and how the procedure compares with medications and investigational exosome protocols. Individual responses vary, protocols differ widely across studies, and the evidence base remains limited.

What PRP is and how it is proposed to work

Platelet-rich plasma is prepared by collecting a small volume of whole blood—typically 10 to 60 milliliters—and centrifuging it to separate red blood cells from plasma. The platelet-poor fraction is discarded, leaving a concentrate with platelet counts three to five times higher than baseline. Platelets contain alpha granules that store growth factors including platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), and insulin-like growth factor-1 (IGF-1). When activated—by calcium chloride, thrombin, or mechanical disruption—these granules release their contents.

The hypothesis is that injecting this concentrate into the scalp delivers a bolus of growth factors to the dermal papilla and surrounding follicular tissue. In laboratory models, PDGF and VEGF have been shown to promote angiogenesis and cell proliferation. Some researchers propose that these signals may prolong the anagen (growth) phase of the hair cycle or reactivate miniaturized follicles. To date, however, the mechanism has not been established in controlled human trials, and the extent to which injected growth factors reach follicular stem cells in vivo remains unclear.

The positive trials: what they found and how small they were

The most frequently cited positive study is Gentile et al. (2015), a half-head randomized controlled trial in 23 men with androgenetic alopecia. One half of the scalp received PRP injections at baseline, one month, and two months; the control side received saline. At six months, biopsies and folliscope counts showed a statistically significant increase in hair density and hair thickness on the PRP side. The mean increase in follicular density was approximately 33 hairs per square centimeter. The authors concluded that PRP may stimulate hair regrowth, but noted the small sample and short follow-up.

Alves and Grimalt (2018) published a randomized trial in 28 men comparing PRP injections plus daily 5% minoxidil and 1 mg finasteride with minoxidil and finasteride alone. At six months, the PRP group showed a greater increase in hair density than the medication-only group. Because all participants were on medication, the study does not isolate the effect of PRP, and the sample size was again small.

Tawfik and Osman (2018) conducted a split-scalp, placebo-controlled trial in 30 women with female pattern hair loss. One half of the scalp received PRP every two weeks for three months; the other half received saline. The PRP side showed a statistically significant increase in hair density and diameter at six months. The authors reported no serious adverse events, but acknowledged the short follow-up and the need for larger, longer studies.

Across these positive trials, sample sizes ranged from 23 to 30, follow-up was six months or less, and protocols varied in platelet concentration, activation method, injection depth, and therapy frequency. None of the studies has been replicated at scale.

The negative and null trials: what did not work

Puig, Reese, and Peters (2016) published a double-blind, placebo-controlled pilot study in 26 women with female androgenetic alopecia. Participants received either PRP or platelet-poor plasma injections every month for three months. The primary outcome was change in hair mass index, measured by phototrichogram. At six months, there was no statistically significant difference between groups. The authors concluded that PRP did not demonstrate efficacy in this study, though they noted the small sample and suggested that different protocols might yield different results.

Mapar et al. (2016) conducted a pilot randomized controlled trial in men with androgenetic alopecia. Participants received PRP or placebo injections every two weeks for three months. Hair pull tests, patient satisfaction scores, and investigator assessments showed no significant benefit in the PRP group. The study was underpowered, and the follow-up period was short, but the null result stands.

Both of these trials used placebo controls—platelet-poor plasma or saline—and blinded assessors. The negative findings suggest that not all PRP preparations or protocols produce measurable hair density changes, and that publication bias may favor small positive trials over null results. The American Academy of Dermatology notes that the evidence for PRP in hair loss remains investigational and that larger, standardized trials are needed.

What the meta-analyses conclude (and why they disagree)

Gupta and Carviel (2017) performed a meta-analysis of 11 studies and reported a pooled increase in hair density in the PRP groups. However, the authors flagged significant heterogeneity in protocols—platelet concentration ranged from 1.5 to 8 times baseline, spin speeds varied, some preparations were activated with calcium chloride and others were not, and the number of sessions ranged from one to six. Follow-up was typically three to six months. The authors concluded that while PRP shows promise, the quality of evidence was low and standardized protocols are essential.

Giordano et al. (2017) reviewed 10 trials and similarly found a pooled benefit in hair density and thickness. They noted that most studies were small, unblinded, or lacked placebo controls, and that the risk of bias was high. The meta-analysis included both randomized and non-randomized studies, which limits the strength of the conclusion.

Evans et al. (2022) conducted a systematic review and meta-analysis of randomized controlled trials only. They found a statistically significant increase in hair density with PRP compared with controls, but again highlighted the small sample sizes, short follow-up, and wide variation in protocols. The authors stated that the clinical significance of the observed changes—often 20 to 40 hairs per square centimeter—is uncertain, and that patient-reported satisfaction did not always correlate with objective measurements.

Gentile and Garcovich (2020) compared PRP with minoxidil, finasteride, and adult stem-cell-based approaches in a systematic review. They noted that finasteride and minoxidil have been studied in large, multi-year randomized controlled trials with consistent protocols, whereas PRP and stem-cell therapies have not. The authors concluded that all three categories—PRP, medications, and stem-cell approaches—may have a role, but that the evidence for medications is stronger and that stem-cell protocols remain investigational.

The meta-analyses agree that PRP shows a pooled benefit in small studies, but they disagree on the clinical importance of that benefit and on whether the heterogeneity in protocols undermines confidence in the findings. None of the meta-analyses recommends PRP as a first-line option over medication.

PRP as an adjunct to a hair transplant

Some surgeons inject PRP into the recipient area at the time of follicular unit extraction (FUE) or into the donor area to promote faster healing. Sindhusen et al. (2025) performed a systematic review of PRP as an adjunct to hair transplantation. They identified eight studies, most of which were small and uncontrolled. A few split-scalp studies suggested faster regrowth or higher graft survival on the PRP side, but the quality of evidence was low and the results were inconsistent. The authors concluded that PRP may have a role as an adjunct, but that larger randomized trials with standardized protocols are needed before it can be recommended routinely.

In practice, many patients undergoing FUE ask about PRP because they hope it will accelerate the visible result. The published data do not show a dramatic difference, and the cost-benefit ratio is uncertain. Some clinics offer PRP as an optional add-on; others do not use it at all. Individual responses vary, and the decision is typically made by the surgeon based on the patient's goals and budget.

Side effects, protocols, PRF and how PRP compares with medication and exosome therapy

PRP is autologous—it comes from the patient's own blood—so allergic reactions are rare. The most common side effects are injection discomfort, transient swelling, and bruising at the injection sites. These typically resolve within a few days. Serious complications are uncommon but include infection and, very rarely, nerve injury if injections are placed too deeply. PRP is not appropriate for people with platelet function disorders, active infections, or certain clotting abnormalities. Patients on anticoagulants may need to discuss timing with their physician.

Protocols vary widely. Some clinics spin blood at 1,500 revolutions per minute for five minutes; others use 3,000 RPM for ten minutes. Some activate the platelets with calcium chloride; others inject the concentrate immediately without activation. Injection depth, volume per site, and the number of sessions (typically three to six) also differ. There is no consensus protocol, and the lack of standardization makes it difficult to compare studies or predict which patients will respond.

Platelet-rich fibrin (PRF) is a variant in which the blood is spun at lower speed without anticoagulant, forming a fibrin matrix that traps platelets and leukocytes. Proponents suggest that the fibrin scaffold releases growth factors more slowly, but there is even less published data on PRF for hair loss than on PRP. Most of the evidence cited above comes from PRP studies.

Compared with finasteride and minoxidil, PRP has been studied in far fewer patients and for shorter periods. Finasteride (1 mg daily) was evaluated in multi-year, placebo-controlled trials involving hundreds of men and showed sustained reductions in hair loss and modest increases in hair count (Gentile & Garcovich, 2020). Minoxidil (5% topical solution) has similar data. Both medications have known side effect profiles—finasteride can cause sexual side effects in a small percentage of men; minoxidil can cause scalp irritation or unwanted facial hair growth in women—but the efficacy data are robust. PRP does not have the same level of evidence.

Exosome therapy and scalp protocols involving stem-cell-derived products are investigational. Exosomes are extracellular vesicles that carry signaling molecules. Early studies in animals and small pilot trials in humans have explored their role in hair follicle signaling, but these products are not FDA approved to treat any disease. The U.S. Food and Drug Administration has issued consumer alerts on regenerative medicine products, including stem cells and exosomes, warning that many marketed products have not been shown to be effective or well tolerated in rigorous trials. Patients considering exosome or stem-cell scalp protocols should understand that the evidence is limited and that these approaches remain investigational.

Springs Rejuvenation offers investigational PRP-type and exosome-based scalp protocols as adjuncts to medication and micrograft procedures. Dr. Charles Pereyra, a board-certified emergency physician and member of the International Society of Hair Restoration Surgery, performs a Follicular Health Assessment to discuss which options most closely fit the patient's goals, hair characteristics, and medical history. Patients interested in learning more may call (888) 503-4482 to schedule an evaluation at one of the clinics in Miami, Los Angeles, Austin, Atlanta, or New York.

Medical disclaimer: Stem cell and exosome therapy is not an FDA approved therapy and is considered to be in the experimental stages; it is not FDA approved to treat any disease. These statements have not been evaluated by the FDA and are not intended to diagnose, treat, cure, or prevent any disease. Individual results may vary. This page is educational and is not medical advice; always consult a qualified physician. Written and reviewed for medical accuracy by Dr. Charles Pereyra, MD, Medical Director, Springs Rejuvenation Hair.