There are few more powerful molecules than dopamine. It rules our lives, gives us pleasure, contributes to our greatest pain and is responsible for our greatest feats. Yet it remains largely unknown by many.

Dopamine is a neurotransmitter, capable of sending messages between neurons in the brain. Neurons containing dopamine (dopaminergic neurons) are responsible for ‘desire’ – that elusive yet unambiguous emotion giving us pleasure and pain.

Essentially any burst of pleasure results in a shot of dopamine into the dopaminergic system connecting our emotional brain (the limbic system) to the rational, decision-making part of the brain (prefrontal cortex). The reengaging in the activity of pleasure reinforces the response. Pretty soon we know what we want and how to get it.

It could be a doughnut, another chocolate, sex, a drug or whatever takes your fancy. The pleasure of closing the deal, a cold beer (or four) at the end of the day or putting another $10 into the slot machine all derive their emotional origins from the resultant dopamine surge in our brains.

Used wisely, dopamine is a powerful friend. It’ll give you the motivation to win the game, to get that last paper out late at night and may even help you find a life partner. Unregulated, it can turn life into a disaster.

Addiction is probably the best example. Psychoactive drugs use dopamine to reinforce their pleasurable effects. In fact they can be referred as reinforcing agents. It’s no coincidence that the most addictive drugs have the greatest reinforcing capacity. Cocaine is the archetypal drug. It directly works on dopaminergic neurons to increase the level of activity in the dopaminergic system. Thus cocaine use results in a strong compulsion to use more cocaine. It essentially hijacks the brain.

Opiates work similarly, though much of their addictive edge comes from the terrible withdrawal system that the user gets after cessation. Using the opiates again relieves these symptoms and so the cycle continues.

Some psychoactive drugs are not heavy reinforcers. Examples are MDMA (ecstasy) and cannabis. Although these drugs do have some reinforcing capacity, it is not great and so dependence is less common than with drugs like heroin and cocaine. Alcohol does have the capacity to reinforce through its effect on the natural opiate centres of the brain to loosen up the dopaminergic system and drive pleasure.

Over time, the dopaminergic pathways in the brain (also known as the reward pathways) build strength and resistance following repetitive substance use. This change in hard wiring is one reason why addiction can be so difficult to overcome, and desire to use the substance of choice may persist all one’s life.

Natural reinforcers such as sex and food are usually regulated by the body. Satiety results in a reduction in appetite and takes the gloss off food. Deregulation of the system, for example in obesity, means that the level of satiety is reset to an unhealthy level. In that case, satiety will not result in stopping eating.

In fact, science has been examining the parallels between natural highs and psychoactive substance use in people addicted to either. It turns out that similar brain changes are seen in individuals with food addiction and obesity compared with cocaine-dependent drug users. MRI scans on both types of individuals show increased activity in the dopaminergic pathways when exposed to the addictive substance, be it cocaine or doughnuts.

In essence, it’s a control issue. Can the pre-frontal cortex summon up all its might to defeat those dastardly surges of emotion in the form of dopamine via the reward pathway? Often not, and we succumb – a pawn in the face of desire.

Liking something doesn’t mean you have an addiction. It has to control your life, you have to need it to get by, you prioritise it over other things such as friends or family. It becomes your focus and life.

The trick is to train ourselves to engage in healthy, mild addictions. Running, exercise, healthy food, engaging in social relationships, our own intimate family relationships ... These are good fodder for the reward pathway, as well as being healthy for our minds and bodies.

So take a moment sometime when you are engaging in something that gives you pleasure. Are you channelling your dopamine neurons in your own interest? For your health? Or have they got the better of you? Are you a victim of your reward pathways?

Dr Nick Walsh is the Chief Medical Officer at the International SOS Clinic in Phnom Penh. He is a member of the Royal Australasian College of Physicians and he has worked in emergency and public health medicine in Australia and Asia for the past 10 years.