You might want to use "will be" instead of "is," since you are speaking about the future instead of the present. Example: "I don't see if there will be a side effect in the future." Secondly, whether you use "don't see" or "can't see" depends on what you are trying to say, since they could mean different things. "I don't see" could mean, "I don't understand." It could also mean "I doubt," as in, "I doubt there will be a side effect in the future." "I can't see," means that you have no way of knowing if there will be a side effect in the future. It would be similar to saying "I can't tell if there will be a side effect in the future." Are you trying to say that the chance of a side effect in the future is unlikely? You might want to say, "I don't think there will be a side effect in the future." It's clearer/more specific. Are you trying to say you have no way of knowing if there will be a side effect in the future? Say, "I can't tell if there will be a side effect in the future." I hope this helps! :)

I would say can't. It better carries the idea of trying one's best to look into the uncertain future. Don't just means flatly "it won't happen".