Richard Roxburgh unpacks the science of our two most commonly used legal drugs - tobacco and alcohol. Science historian Professor Robert Proctor reveals how our nicotine habit transformed into such a lethal addiction.

Cannabis, psychedelics and MDMA are all experiencing a research renaissance, as scientists reach new understandings of their interaction with the human body and mind.

We look at the different effects of caffeine, cocaine and methamphetamine. Two-time world surfing champion Tom Carroll opens up about his own battle with addiction and how he got clean.

The finale examines the opioid crisis in the United States and looks at diseases caused by poor diet and sugar addiction.