Sclerotherapy is a very safe procedure. That’s why it has been used for almost 90 years! Still, there are some potential side effects with sclerotherapy:
Skin discoloration, a darkening of the skin, may occur at the injection sites, but it usually resolves in a few weeks.
Itching, burning, and pain at the injection sites for a couple of days
Bruising
Allergic reaction to the sclerosant
More serious risks are very rare but include possible blood clot formation, nerve damage, and air bubbles in the treated veins.