How Many PRP (Platelet-Rich Plasma) Sessions Are Used, and When Might Results Show?

Platelet-Rich Plasma (PRP) therapy is increasingly discussed in the context of hair restoration. This treatment involves collecting a small amount of a patient’s blood, processing it to concentrate the platelets, and injecting this plasma into the scalp. Platelets are specialized cells in the blood known for their role in healing, primarily by releasing growth factors that can stimulate cell regeneration. These growth factors are thought to encourage hair follicles to enter the anagen phase, or active growth phase, potentially increasing hair density and thickness.

The process of PRP therapy is not merely cosmetic. The growth factors present in platelets, including platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), and transforming growth factor-beta (TGF-β), are thought to support angiogenesis, the formation of new blood vessels, and to influence stem cells in the hair follicle bulge. However, these effects are still being explored and the optimal concentration, injection technique, and session frequency remain subjects of ongoing research.

When Hair Growth Becomes Noticeable

Clinical trials show which schedules have been tested, not a proven best schedule. In 2015, Gentile and colleagues in Italy ran a randomized, evaluator-blinded, placebo-controlled half-head trial in men with pattern hair loss (23 enrolled, 3 excluded). PRP was injected on one half of the scalp and placebo on the other, in three sessions 30 days apart. After the third session, the authors reported a mean increase of 33.6 hairs in the target area and 45.9 hairs per cm² in total hair density compared with baseline; the abstract does not give the difference from the placebo side. Four patients had progressive hair loss again after 12 months and were re-treated (Gentile et al., 2015). Results were measured after the third session. The trial was small and included only men.

Alves and Grimalt (2016) ran a randomized, placebo-controlled, double-blind half-head study in 25 patients with androgenetic alopecia, with three PRP sessions one month apart. Six months after the first session, hair density was higher on the PRP side than on the placebo side.

A 2023 meta-analysis of 9 randomized trials (238 patients) found higher hair density with PRP than with placebo at 3 and 6 months, but no significant difference from placebo in hair count or hair thickness (Zhang et al., 2023).

Variables Influencing Response

Patient-specific factors are thought to shape outcomes. Age, health status, severity and pattern of hair loss, and the remaining density of hair follicles are influential. Clinicians often say that people in early stages of thinning respond better, but this has not been well tested. Chronic illnesses, hormonal imbalances, and lifestyle factors such as diet, smoking, and stress may impede results. Additionally, the concentration of platelets in PRP preparations varies, potentially affecting efficacy. Differences in centrifugation protocols, injection depth, and volume can alter growth factor availability, illustrating why treatment response is not uniform.

Session Frequency, Duration, and Expected Progress

There is no standard schedule. Protocols used in trials usually involved about three sessions roughly one month apart, with results measured 3 to 6 months after starting; some clinics add maintenance sessions, but their timing has not been compared in trials. Your clinician will set the schedule. Results, when they occur, are gradual.

Research Assessment and Critical Analysis

Despite its popularity, PRP therapy lacks large-scale, long-term studies. The evidence is limited by small sample sizes, variability in protocols, and short follow-ups. A 2017 meta-analysis by Gupta and Carviel found 13 studies but could pool data from only four trials (60 participants). It described PRP as an off-label treatment and the evidence as preliminary.

PRP for hair loss is off-label. The devices used to prepare PRP are FDA-cleared for processing blood, but no PRP product is FDA-approved to treat hair loss (Gupta & Carviel, 2017; Paichitrojjana & Paichitrojjana, 2022). Reported side effects are usually mild and temporary: pain during the injections, mild headache, itching, redness and swelling of the treated area (Paichitrojjana & Paichitrojjana, 2022). The same review lists platelet disorders, a very low platelet count and infection at the injection site as reasons not to have PRP. Anyone taking blood-thinning (anticoagulant or antiplatelet) medicines or anti-inflammatory painkillers should tell the clinician before treatment, because these affect bleeding and platelet function; never stop a prescribed blood thinner without advice from the prescribing doctor.

Overall, trials have usually given about three monthly sessions and measured results after 3 to 6 months. They do not establish how many sessions any one person needs. Response varies widely, and PRP is not a guaranteed fix.

References

Alves, R., & Grimalt, R. (2016). Randomized placebo-controlled, double-blind, half-head study to assess the efficacy of platelet-rich plasma on the treatment of androgenetic alopecia. Dermatologic Surgery, 42(4), 491–497. https://pubmed.ncbi.nlm.nih.gov/27035501/

Gentile, P., Garcovich, S., Bielli, A., Scioli, M. G., Orlandi, A., & Cervelli, V. (2015). The effect of platelet-rich plasma in hair regrowth: A randomized placebo-controlled trial. Stem Cells Translational Medicine, 4(11), 1317–1323. https://pubmed.ncbi.nlm.nih.gov/26400925/

Gupta, A. K., & Carviel, J. L. (2017). Meta-analysis of efficacy of platelet-rich plasma therapy for androgenetic alopecia. Journal of Dermatological Treatment, 28(1), 55–58. https://pubmed.ncbi.nlm.nih.gov/27152474/

Paichitrojjana, A., & Paichitrojjana, A. (2022). Platelet rich plasma and its use in hair regrowth: A review. Drug Design, Development and Therapy, 16, 635–645. https://pubmed.ncbi.nlm.nih.gov/35300222/

Zhang, X., Ji, Y., Zhou, M., et al. (2023). Platelet-rich plasma for androgenetic alopecia: A systematic review and meta-analysis of randomized controlled trials. Journal of Cutaneous Medicine and Surgery, 27(5), 504–508. https://pubmed.ncbi.nlm.nih.gov/37533146/