I have rapid changes is mood, up and down and up and down. I am on Lamictal. It still can happen but it is manageable now, and does not happen as often.

Lamictal is known to be a prophylaxis that is taken to help prevent cycling. It also has antidepressant properties. The studies on rapid cycling are positive but IMO not enough to tell for certain its efficacy (reliability) with people who have this problem.

Like the other posted mentioned, rapid changes in mood is also a symptom of BPD. I think therapy can help in this situation.