Throughout the series (thus far), Detective Cohle has exhibited all of these symptoms at some point, such as showing up to Detective Hart's for dinner in a rundown state and with a depressed affect. In addition to dysthymia, by his own admission, Cohle is battling addiction to substances, especially alcohol and stimulants (probably to self-medicate). Cohle started using while an undercover narcotics investigator in Texas but found he could not stop. Cohle is able to stay sober at the beginning of the series but as the investigation into the "Yellow King" and "Carcosa" cult deepens, so does his cravings and his inability to resist his desires. At the same time, it is clear Cohle is an incredibly intelligent and astute investigator.
Again, this interests me since I have worked with so many interesting and intelligent people battling depression through self-medication via alcohol and stimulants. Stress and triggers have a huge impact on a person's ability to stay sober and healthy. I am always excited to see an accurate depiction of mental illness on television. It is very important in normalizing an experience that many people struggle with at some point in their lives. The stigma surrounding mental illness keeps this issue in the dark and we need to do more to help bring people out of this darkness and into appropriate treatment.
Unfortunately, people with mental illness are still viewed as aberrations and highly dangerous. I hope True Detective continues to explore mental illness. I have a feeling things aren't going to end well for either characters. However, I am grateful for being able to watch an interesting and competent protagonist struggle with demons that many in the real world struggle with as well.