All you need to know about the stress hormones

Find out more about adrenaline, noradrenaline, and cortisol – the three major hormones responsible for the stress response.

When you’re stressed, the level of various hormones in your body change. Reactions to stress can increase the mobilisation of energy sources, helping you adapt to the situation at hand.

You may experience stress in a situation that disturbs the equilibrium between you and your environment. When stressed, your body is likely to activate its sympathetic nervous system and enter the flight or fight response [1].

We look at the three major hormones that are responsible for the stress response.

Fight or flight vs rest and digest

The autonomic nervous system is the part of the peripheral nervous system that controls the stress response and involuntary processes, such as regulating blood pressure and heart rate [2].

The three divisions of the autonomic nervous system [2]:

  • The sympathetic nervous system
  • The parasympathetic nervous system
  • The enteric nervous system

The sympathetic nervous system

The sympathetic nervous system is often known as the fight or flight response. Once this response is triggered, our level of activity and attention increases.

Sympathetic response:

  • Heart rate speeds up
  • Blood pressure rises
  • More sugar becomes available as fuel
  • Unnecessary functions, such as digestion, are reduced [3].

The parasympathetic nervous system

The parasympathetic nervous system is the rest and digest or the feed and breed response [4].

Parasympathetic response:

  • Heart rate slows
  • Breathing slows
  • Blood pressure reduces
  • Healing and digestion increase
  • Fertility and libido increase

The enteric nervous system

When a person becomes stressed enough to trigger the stress response, the enteric nervous system works with the gut to slow digestion down or speed it up.

If the enteric nervous system is in overdrive, a person may experience abdominal pain and other symptoms of gastrointestinal disorders [5].

These three divisions all work together to put your body into the stress response.

How does the stress response work?

Once the amygdala (the part of the brain that drives the stress response) has alerted the hypothalamus (the part of your brain that controls most of your bodily functions) of the stressful trigger, it activates the sympathetic nervous system and triggers the adrenal glands.

The adrenal glands, located on top of the kidneys, are responsible for:

  • Regulating blood pressure and metabolism
  • Releasing the three hormones involved in the stress response

The three main hormones responsible for the stress response are:

  1. Adrenaline

Adrenaline is a hormone which is secreted into the blood stream to act on other cells in the body. Have you ever been woken from sleep by a loud or unfamiliar noise? You suddenly have a surge of energy, all your senses are on high alert, your muscles are tense, your heart is pounding, your hearing and vision sharpened. You are ready to flee or fight. That immediate reaction is all thanks to adrenaline.

  1. Noradrenaline

Noradrenaline is mostly used as a neurotransmitter in the sympathetic nervous system, to communicate between neurons, although a small amount is secreted into the blood stream. This hormone is a team-mate to adrenaline. It heightens your focus and improves your responsiveness. It helps improve blood flow to the essential organs and diverts it away from less essential functions during the stress response.

  1. Cortisol

Once the adrenaline release starts to slow, the hypothalamus then triggers the second part of the stress response.

  • If the brain continues to sense stress, the hypothalamus releases the corticotropin-releasing hormone (CRH).
  • CRH travels to the pituitary gland, causing it to release the adrenocorticotropic hormone (ACTH).
  • ACTH then goes to the adrenal glands triggering the release of cortisol [6].

Cortisol is a steroid hormone and is often known as the stress hormone.

Cortisol is responsible for regulating:

  • Blood pressure
  • Blood sugar levels
  • Metabolism
  • Inflammation
  • Aiding in tissue repair

Cortisol also curbs functions that could be detrimental in a fight or flight situation, such as the immune and digestive systems, the reproductive system, and growth processes.

The perfect amount of cortisol can be lifesaving when in survival mode. Short term, cortisol can help to develop resilience and perform well in challenging situations.

However, these days, stress is more of a way of life for many people.

When your body is in a constant state of stress, the sympathetic nervous system is continually activated. Continual high levels of cortisol levels can lead to an increased risk of serious health implications over time.

Chronic stress with raised cortisol levels can lead to:

  • A reduced immune function
  • Higher blood pressure
  • Anxiety
  • Depression
  • Digestive problems
  • Insomnia

High levels of cortisol can also cause fat to be stored around the organs in the abdomen (visceral fat), which increases the risk of cardiovascular disease and diabetes [7].

You can read more about the effects of chronic stress in our what does stress do to the body section.

Stress and exercise

Over-exercising or exercising at a very high intensity (such as lifting very heavy weights) can cause chronically high levels of cortisol.

If cortisol levels are extremely high, it can have similar effects on the body to chronic stress. Therefore, putting you at higher risk of health conditions such as cardiovascular disease.

High levels of cortisol can also hinder the results of exercise, as it can cause the body to hold onto fat around the middle – a common side effect.

How do I know my body’s stress level?

Whether from intense over-exercising or chronic stress, the long-term activation of the stress-response system can disrupt the body’s processes.

If you think you may have high cortisol levels or want to see if your stress levels are affecting your health, body, and mind – it may benefit you to test your cortisol or blood biomarkers for general wellbeing.

Our Cortisol Saliva Stress Test can help you understand your stress levels and adrenal function throughout the day.

To look at your overall wellbeing, our Advanced Well Man Blood Test and Advanced Well Woman Blood Test checks biomarkers for energy, wellbeing, and long-term health.


  1. Ranabir, S. and Reetu, K., 2011. Stress and hormones. Indian Journal of Endocrinology and Metabolism, 15(1), p.18.
  2. Waxenbaum JA, Reddy V, Varacallo M. Anatomy, Autonomic Nervous System. 2021 Jul 29. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan–. PMID: 30969667.
  3. Alshak MN, M Das J. Neuroanatomy, Sympathetic Nervous System. 2021 Jul 26. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan–. PMID: 31194352.
  4. Tindle J, Tadi P. Neuroanatomy, Parasympathetic Nervous System. 2020 Nov 15. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2021 Jan–. PMID: 31985934.
  5. Harvard Health. 2021. Stress and The Sensitive Gut - Harvard Health Publishing - Harvard Health. [online] Available at: <> [Accessed 21 December 2021].
  6. hormone, A., 2021. Adrenocorticotropic hormone | You and Your Hormones from the Society for Endocrinology. [online] Available at: <> [Accessed 21 December 2021].
  7. van der Valk, E., Savas, M. and van Rossum, E., 2018. Stress and Obesity: Are There More Susceptible Individuals?. Current Obesity Reports, 7(2), pp.193-203.

Related tests

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