How common is shock loss after PRP?

PRP is used to stimulate hair growth, not cause it. Shock loss is due to the loss of normal hair whether it is from donor site or recipient area.  It can occur with both FUE and strip procedures.  Usually if it occurs it will take place in the recipient area.  
Shock loss from hair transplant can occur due to the following:
Anesthesia-  excessively long procedures taking longer than 12 hours can induce shock loss more likely.  the repeated use of lidocaine, marcaine, and perhaps most importantly epinephrine can affect nourishment of the hairTraumatic harvest-  In strip surgery, traumatic harvest can induce shock loss.  Recipient area trauma- during the incision making process the hairs are either crushed or cut and damaged during the process. 
Ways to minimize shock loss are as follows:
Improve recipient bed and donor area environment.  Make your recipient environment improved by addition of growth factors and/or PRP to help reduce incidence of shock loss to native hairs.Use of Rogaine and Propecia- can help miniaturized hair become more stable and less likely to fall out during procedure9xRobotArtas-  The latest version of the robot can make recipient sites and can determine angle of existing hair and help ensure that the angle will not damage existing hair.  Especially helpful in patients where you are transplanting hair to create densityMinimize anesthesia time and procedure time- We limit number of grafts to a safe number per session.  Extended anesthesia periods and harvest times can cause patients to have a higher chance of shock loss.  The 9x Robot harvests between 1000-1500 grafts per hour making it superior to previous additions and traditional FUE approaches.Best,
Anil Shah

There are several variables that could influence shock loss  after PRP.  The incidence of shock loss using  pure PRP without extracellular Matrix is low. However, injection technique and anesthesia technique makes a difference. If the subdermal  Depo injection technique is used, without ECM or additional anesthesia, I find that shock loss is very uncommon. PRPHAIRMD.COM 

There is sufficient theoretical scientific basis to support the use of PRP in hair loss but clinical studies are limited to date.Shock hair loss is not commonly associated with PRP therapy.

Thank you for your questions. "Presently, there are limited published data regarding PRP's potential effect on hair." But we have some data on PRP:"
Study of Platelet-Rich Plasma Injections in the Treatment of Androgenetic Alopecia Through an One-Year Period"PRP promotes differentiation of stem cells into hair follicle cells,prolong  hair growth cycle( anagen phase), increase cell survival ( by inhibiting apoptosis-cell death) , and increase perifollicular blood circulation. Therefore, it is a useful tool for male type of boldness(androgenetic alopecia). You can read more
"Hair-shock" is not common with PRP Treatment . It happens when you start or stop Minoxidil Treatment .