Many presription and over the counter medication thin the blood and make bruising much more likely with under eye Restylane treatment. Herbal products are also likely to thin the blood. Even the grapefruit juice in the South Beach diet seems to increase the risk of bruising.
I would recommend that you contact the office where you plan to be treated and get from them their list of medication to avoid. Avoiding these will reduce the chance that you might bruise. However, you can still bruise. Any time you are poked with a needle there is a risk of bruising. This can be a little dot on the skin--no big deal. Or it can be a massive black eye and in our society it is presumed that you are the victim of domestic violence. These types of bruises can last up to 3 weeks. The risk of this type of bruising is about 1 to 2 per hundrend.
Think about undereye Restylane as though it is surgery for the lower eyelid that you just happen to get with a needle. The results can last a couple of years but you definitely want to avoid doing treatment right before a big social event.
Now the important but. If you are on a medication that thins your blood by order of your physician, do not stop this medication without first consulting the doctor who told you to take this medication. This can include medicines like aspirin, Plavix, and coumadin. This medication are used to control clot formation in very specific conditions so seek guidance from you primary care physician before discontinuing these drugs.