It is very common for people who have used street drugs to wonder if the drugs may have caused their symptoms.
Street drugs can cause many symptoms that can be found in mental illnesses, such as hallucinations, feelings of unreality, paranoia, and both extremely high and low moods. Because of this, it can be difficult or impossible to accurately diagnose (or treat) mental illness in someone who is also using street drugs.
However, there is very little evidence to suggest that using street drugs can cause bipolar disorder in someone who would have otherwise never developed it. For example, a large percentage of Americans use or have used street drugs, and only a relatively small percentage develop bipolar disorder after such use. On the other hand, it is not uncommon for there to be an apparent association between use of street drugs and development of bipolar disorder. In this situation, most likely one of the following 3 things is happening:
Pure coincidence, no causal relationship
The use of street drugs was a form of self-medication in response to already developing symptoms of bipolar disorder
The drugs may have caused someone who was "destined" to develop bipolar disorder to develop the illness a little sooner.
Therefore, I counsel patients not to blame their past street drug use for the development of their bipolar disorder. However, I do use their diagnosis of bipolar disorder as an opportunity to address any ongoing street drug use. In these situations, I try to impress upon patients the understanding that while some people can use street drugs and alcohol with no obvious ill effects, people with bipolar disorder are at much greater risk for suffering adverse effects from these substances. Avoiding drugs and alcohol falls under the category of "babying your brain, (see number 6)."
In general, current ideas about how mental illnesses like bipolar disorder develop recognize that there are people who have a greater genetic likelihood than others to develop mental illnesses. Unknown environmental factors (of which street drug use may be one) can further increase the chances or cause an earlier disease onset.
In summary, there are so many unknowns about the causes of bipolar disorder that it is not worth torturing oneself by believing that use of street drugs alone caused one to develop bipolar disorder.