What is rapid cycling? Rapid cycling means that someone will experience many episodes of illness each year. How many episodes? Well the cut off is essentially arbitrary, but it is taken to be four or more episodes of mania and depression in any one year period. Some people have very rapid switches and in these cases the terms ultra-rapid (days) and ultra-ultra rapid or ultradian (within a day) cycling have also been used. The diagnosis of rapid cycling is not used by everybody and is not included in all classification systems. For example, although it is included in the American diagnostic system (DSM-IV ) it is not currently part of the international classification system, ICD10. Is it easy to distinguish rapid cycling from other conditions? The diagnosis of rapid cycling bipolar disorder can be difficult. In adolescents it can be mistaken for conditions such as ADHD. In adults, it may be difficult to distinguish very fast cycling patterns from the mood instability found in borderline personality disorder. We know that many people find that it takes far too long before they receive a bipolar disorder diagnosis, something confirmed by Bipolar UK’s recent survey. It is therefore vital that a full assessment is made to ensure that a diagnosis of rapid cycling bipolar disorder is not missed, or indeed, that a label of rapid cycling is not wrongly applied to another condition. ‘There is still a lot we don’t know about rapid cycling — does it represent a separate type of bipolar disorder, or merely reflect bipolar disorder that is not receiving optimal treatment?’ How common is rapid cycling? About 10 to 20 per cent of people with bipolar disorder may have rapid cycling and it is probably more common in people with the form of bipolar disorder sometimes referred to as bipolar II (those that experience less severe highs). It is also the case that rapid cycling is more common in women. Is rapid cycling a subtype of bipolar disorder? There is still a lot we don’t know about rapid cycling – does it represent a separate type of bipolar disorder, or merely reflect bipolar disorder that is not receiving optimal treatment? Although many may no longer experience rapid cycling when they find the combination of medication and self- management that suits them, some people will continue to have many episodes of illness despite adequate treatment. What is clear is that rapid cycling is a transient phenomenon for most people — many people with bipolar disorder will experience periods of rapid cycling at certain times but have other times, when this label would not apply. Why is rapid cycling important? It is important because it may pick out a form of bipolar disorder that responds less well to medication. Studies have suggested that people with rapid cycling have a poor response to treatment. Although the first study to show this was of lithium treatment, it is probably true for other medications too. What makes rapid cycling more likely? It may be that for some people, treatment with antidepressant medication alone can increase the chances of developing rapid cycling. That is one of the reasons why many clinicians will recommend that antidepressants, when used in someone with bipolar disorder, are used in combination with a mood stabilising medication such as lithium. It may also be the case that certain antidepressants, for example the ‘tricyclics’, are more likely to result in rapid cycling than other antidepressants such as the ‘SSRIs’. What is certainly true is that antidepressants, when taken with a mood stabiliser, are much less likely to result in rapid cycling.