There are other mental disorders besides bipolar disorder, which can produce mood swings. For example, mood swings can be caused by general medical conditions or other physical illnesses that affect the body's regulatory systems. Suspect medical conditions include various brain chemical imbalances, hormone disorders (such as hyper- or hypothyroidism), bacterial or viral infections, and autoimmunity conditions (leading to body rhythm dysregulation). Such illnesses could cause people to experience bipolar-like mood swings even though they don't have actual bipolar disorder. See our section on Contemporary Understandings of Bipolar Disorder for a more detailed discussion of medical conditions, which must be ruled out prior to bipolar diagnosis.
Equally confusing is the use of street drugs and/or alcohol, which can lead to altered mood states. Intoxication with central nervous system stimulant drugs (such as Cocaine, or Methamphetamine) can easily mimic a manic state. Similarly, intoxication with central nervous system depressant drugs (such as alcohol, or Valium) can mimic a depressive state. When it is not clear if a mood condition is due to a drug or to a disease process, doctors will tend to hold off making definitive bipolar diagnoses until enough time has passed so as to allow any drug effect that might be affecting mood to metabolize and clear out of the affected person's system.
As previously mentioned, manic people tend to show poor judgment and to be pleasure-seeking in the extreme. For this reason, it is not at all uncommon for people in the midst of a manic disorder episode to take drugs and/or drink alcohol. Similarly, people experiencing a depressive episode tend to feel awful, and sometimes will "self-medicate" with street drugs and/or alcohol in an attempt to help themselves feel better. . Though some short-term relief may be gained by such self-medication attempts, substance abuse and addiction problems can result in the long-term, which compounds the existing mental disorder. Addicts, of course, are at the mercy of the availability of their drugs; they may develop manic depressive mood symptoms as a result of withdrawal symptoms, or efforts to ward off experiencing withdrawal symptoms. When either of these situations occur, you have a situation where a true bipolar condition and drug effects may exist simultaneously. Once again, this sort of situation can be ruled out by a diagnosing doctor by simply letting enough time pass for the effects of any drugs or alcohol to wear off.
There is perhaps a weak bi-directional causal relationship between substance abuse disorders and bipolar disorder. People who have bipolar affective disorder have an increased risk for developing substance abuse problems, and people who use substances may help to release whatever inborn potential or vulnerability they may have for developing bipolar disorder (see our section on the Diathesis-Stress Hypothesis for more detail). Whatever the true relationship is between bipolar conditions and substance abuse, it is not in question that the combination of the two conditions leaves people worse off than either alone.
Complicating bipolar diagnosis further is the possibility that an individual with mood swings is suffering from a mental illness other than bipolar disorder. A number of other mental disorders are associated with mood swings. Mental disorders which may be commonly confused with bipolar disorder include Borderline Personality Disorder , Schizoaffective Disorder, Unipolar Depression, and Premenstrual Dysphoric Disorder.