Sluggish cognitive tempo (SCT) is a syndrome related to attention deficit hyperactivity disorder (ADHD) but distinct from it. Typical symptoms include prominent dreaminess, mental fogginess, hypoactivity, sluggishness, staring frequently, inconsistent alertness and a slow working speed. SCT has been a subject of controversy for decades and debate about its nature still continues. But it is clear now that this set of symptoms is important because it independently has a negative impact on functioning (such as a diminished quality of life, increased stress and suicidal behaviour, as well as lower educational attainment and socioeconomic status). The SCT symptoms are clinically relevant as they seem linked to a poor treatment response to methylphenidate. Originally, SCT was thought to occur only in about one in three persons with the inattentive subtype of ADHD, and to be incompatible with hyperactivity. But new studies found it also in some people with the other two ADHD subtypes – and in individuals without ADHD as well. Therefore, some psychologists and psychiatrists view it as a separate mental disorder. Others dismiss it altogether or believe it is a distinct symptom group within ADHD (like Hyperactivity, Impulsivity or Inattention). It even may be useful as an overarching concept that cuts across different psychiatric disorders (much like emotional dysregulation, for example). If SCT and ADHD occur together, the problems add up: Those with both (ADHD + SCT) had higher levels of impairment and inattention than adults with ADHD only, and were more likely to be unmarried, out of work or on disability. But SCT alone is also present in the population and can be quite impairing in educational and occupational settings, even if it is not as pervasively impairing as ADHD. Some have encouraged the use of a term such as concentration deficit disorder (CDD) or cognitive disengagement syndrome (CDS) instead of SCT because it may be more appropriate and less derogatory. Signs and symptoms ADHD is the only disorder of attention currently defined by the DSM-5 or ICD-10. Formal diagnosis is made by a qualified professional. It includes demonstrating six or more of the following symptoms of inattention or hyperactivity-impulsivity (or both). The symptoms must also be age-inappropriate, start before age 12, occur often and be present in at least two settings, clearly interfere with social, school, or work functioning, and not be better explained by another mental disorder. Based on the above symptoms, three types of ADHD are