Hi. Ultherapy is a fantastic treatment, but only works best when given plenty of time to fully correct. I would not recommend doing a treatment any sooner that 6 months after your previous treatment. As for side effects, there should not be any, other than the usual side effects seen with the first treatment.
All of these procedures can be performed multiple times, but 99% of the time they probably are not needed. Results will occur over time and patients need to wait around 6-9 months to see the final results. But treating a second time at that point is fine if the patient and physician agree.