What's the Risk of Hydroquinone?

Please, I would like to understand the real risk of hydroquinone, some ones say it may cause cancer, some ones say there is a risk only if it's used for long time ( what long time means??). Is there risk when we use it for 3 or 4 months and stop a month or 2 and then reuse it again. I have another concern too, I'm from Texas and they don't provide it any more in Texas even with a physician prescription, is this because of the risk or there is another raison? Thank you in adavance.