I have hyperthyroidism. Is schlerotherapy safe for me? Will there be side effects in patients with hyperthyroidism?

I do not think you will have any problems with sclerotherapy related to underlying hyperthyroidism.  Just make sure you seek treatment with a qualified board-certified physician for best results.

There should be no problem with you undergoing injection sclerotherapy treatments for spider veins with a history of hyperthyroidism. There are no known side effects that would be directly related to this condition. However, obviously, making sure your condition is under reasonable control, and your body is relatively healthy will ensure you get the best possible results from treatment, and minimize any potential difficulties.