I'm a male looking into PRP treatments for hair loss, what side effects should I be aware of?

PRP (from an anecdotal perspective) has proven to be an effective tool in the arena of hair restoration both as an adjunct to grafting as well as standalone treatment for those who may not (yet) be a candidate for grafting. Patients have demonstrated slowed loss, thickening of existing hair and regrowth. The typical duration of effect is 6-9 months with most patients being treated 2x yearly (at least initially).
Ultimately, whether or not PRP will be effective will depend upon your diagnosis. Some causes of hair loss will respond better to other medical/chemical/surgical therapies. PRP is by no means a magic bullet.With regards to your specific questions, there have been no documented issues related to fertility. PRPis simply a concentration of patient donor plasma which is then reintroduced into the scalp. Side effects are generally limited to those associated with the blood draw and re-injection.
As always, discuss your concerns with a board certified plastic surgeon (ABPS) with experience in hair restoration. 

Platelet  rich plasma utilizes your own blood and no other drugs or agents. The major side effect is soreness. It's important to go to an expert so that it can be prepared properly with a minimal amount of red and white blood cells. Furthermore the injection technique is critical. The subdermal depo injection technique has been validated in clinical studies by Hausauer to produce results.

PRP (Platelet rich plasma) therapy for hair loss uses your own platelets to rejuvenate the hair follicles. This procedure does not use hormones and should have no impact on fertility. The platelets act locally and improve circulation, decrease inflammation and can rejuvenate the hair follicle. 

Hi, and thanks for the question.
I have extensive experience using PRP for cosmetic purposes and am not
aware of any negative side effects regarding fertility or regarding having
children. Like any medical procedure, PRP treatments can result in short-term
aggravations, but even these issues are typically minor. I do not believe you
should be concerned about fertility or abnormalities in procreation related to
PRP.

The side effects are local pain from the injections.  I use a Zimmer cold air blowing machine to lessen the pain.  Tylenol is also helpful.  
The injection sites will also be visible for a few days and then should resolve.  If microneedling is also part of the procedure (which I add to increase the migration of growth factors to the area) then these sites will also heal in a few days.

I wouldn't be to concerned with fertility risks but injecting PRP into the scalp. Possible risks of this procedure include but are not limited to: bruising, swelling, injection site pain, infection can all happen. Its important to go to a good injector and take care of the site after treatment to ensure best outcomes. 

The side effects of PRP include: pain with injections, temporary swelling in the forehead, hair shedding, tenderness for a few days. Other side effects are rare. It does not affect fertility but I do not recommend my own female patients have PRP if trying to conceive.

PRP injections involves removal of your own blood, removing some components and then injecting it into the scalp.  It's your own blood, so there are no issues with fertility.  You may have some transient tenderness in the scalp, and occasionally some swelling, but no issues with having children.

Thank you for your question. You are asking if PRP treatments for hair loss pose any risk for having children and birth defects.
I can certainly give you some guidance about this. I’m a Board Certified Cosmetic Surgeon and Fellowship-trained Oculoplastic Surgeon. I’ve been in practice in Manhattan and Long Island for over 20 years. I’ve been performing hair transplants since I started my practice. I’m also the founder of TrichoStem Hair Regeneration Centers, based on a system we developed that uses extracellular matrix and PRP for non-surgical treatment of pattern hair loss for men and women since 2011. We have patients from around the world who come to see us for this treatment.
PRP alone will not affect fertility or cause birth defects. PRP, or platelet-rich plasma, is taken from your own blood. It’s the concentration of wound healing and growth factors necessary to heal cuts. There is nothing in PRP that can cause any of the side effects you are fearful of.
However, PRP alone, or even a PRP combination treatment like Hair Regeneration may not be enough to treat your pattern hair loss effectively. PRP alone for hair loss is limited to stimulating short-term hair growth, and at least several sessions are required to achieve this. Many patients come to see us because of getting several sessions of PRP injections, but they still don’t see results. Our Hair Regeneration treatment uses PRP as the activator of extracellular matrix to thicken thinning hair and stimulate hair growth from dormant hair follicles. Hair Regeneration is not repeated often to get results, as some older male patients with late onset of hair loss and less DHT-sensitivity can get 3-5 years of sustained benefit, or sometimes even longer, after just one treatment session, and without finasteride. Some patients receive as second treatment as 1-2 years after the first treatment. Younger male patients who start pattern hair loss early, say in their 20s, are more DHT-sensitive. The Hair Regeneration treatment alone can still thicken their thinning hair, but without a DHT-blocker like finasteride, results can’t be sustained as long as older patients with less DHT-sensitivity. I would prescribe finasteride to younger male patients along with the Hair Regeneration treatment to sustain results as long as possible, and to block DHT as the Hair Regeneration treatment is not a DHT-blocker. I assume you are a younger patient with early onset of hair loss as you indicate planning a family in the future.
Finasteride does carry a risk of sexual side effects, but it is exceedingly rare at about 2% of patients. Erectile dysfunction and sperm quality are part of these risks, but again, they are very rare, and the vast majority of patients do not have them. However, since you ask about the fertility risks, they should be mentioned.
I suggest you discuss risks of finasteride with your doctor, as injection treatments alone are not enough to manage aggressive pattern hair loss in young men. The risks are very small, but you will have to decide on accepting these low risks, or not treating your pattern hair loss fully. I hope you found this information helpful. Thank you for your question.