Dopamine is a so-called messenger substance or neurotransmitter that conveys signals between neurons. It not only controls mental and emotional responses but also motor reactions. Dopamine is particularly known as being the "happy hormone." It is responsible for our experiencing happiness. Even so-called adrenaline rushes, such as those experienced when playing sport, are based on the same pattern. Adrenaline is a close relative of dopamine. However, serious health problems can arise if too little or too much dopamine is being produced. If too few dopamine molecules are released, Parkinson's disease can develop, while an excess can lead to mania, hallucinations and schizophrenia.