The effect of hormones of human behaviour


  • Testosterone – a sex hormone found primarily in males – They are released by glands and are responsible for development both before and after birth. At 6 weeks, they are released to form the male sex organ and in teenage years produce secondary sex characteristics such as increased bodily hair and a deeper voice. The brain of a male thus develops differently to that of a female, with superior visual spatial and maths skills. Many studies have shown that testosterone contributes to increased aggressive traits: in a double blind trial Tricker et al (1996) gave two sets of participants 600mg of either testostorone or a placebo and found that those who has been given the hormone scored as more aggressive on a questionnaire. Similarly, Dabbs et al studied prisoners and in his large sample of 700 found that those who possessed higher testosterone levels commited more crimes (mainly of a sexual and violent nature) and broke more rules than the other, who engaged in other types of crime such as theft.
  • Estrogen – a sex hormone found primarily in females – During puberty they are released by the ovaries, providing a suitable environment for the embryo. They increase motor skills (Hampson and Kimura 1988) and during the secondary response at puberty it makes skin softer and hair finer. Whether or not it causes anxiety, depression and irritability is debatable and studies support either side of the argument – self report studies have found that a woman’s mood increases after menopause but Golombok and Fivush (1994) state that there is no consistent evidence as their more methodologically sound daily self report records diminished the typically used retrospective records
  • Oxytocin – the ‘love’ chemical – found in the hypothalamus’ pituitary gland, it is secreted at intimate moments and solidifies an attachment bond following sexual intercourse. It increases contraction of the uterus during child birth, along with an inducement of parental behaviour, and secretion of milk during breast feeding. Klaver et al (2009) gave participants a nasal spray containing either oxytocin or a placebo and found that those who had the oxytocin nasal spray remembered a greater number of faces after one day than the other group, suggesting an increased attachment.
  • Melatonin – causes drowsiness and lowers body temperature to allow sleep. It also increases REM sleep and thus vivid dreaming. It improves sleep in people with intellectual disorders such as autism.  Low melatonin levels have been found to increase the risk of type 2 diabetes. It aids learning and memory and is effective in relieving cluster headaches, migraines and some mood disorders,
  • Thyroxin – increases the rate of reflex actions. Motor and cognitive functions of offspring are impaired following a thyroxin deficiency in mothers.
  • Dopamine – In the brain, it acts as a neurotransmitter to send signals to other nerve cells. The brain includes several distinct dopamine systems, one of which plays a major role in reward-motivated behavior (rewards include food, sex and any neural stimuli that becomes associated); most types of reward increase the level of dopamine in the brain. In addition to being rewarding, dopamine is also arousing — it produces a general increase in movement of all sorts. Despite strong evidence suggesting that dopamine is related to rewards, dopamine release can be caused by events that do not seem to have anything to do with reward, most notably pain. One of the most popular alternatives to the reward theory is the incentive salience theory, which argues that the function of dopamine is to increase the effects of motivators of all sorts, both positive and negative. It has also been found to elevate higher cognitive functions. Abnormally high dopaminergic transmission has been linked to psychosis and schizophrenia.

Parkinson’s disease is a disorder characterized by stiffness of the body, slowing of movement, and trembling of limbs when they are not in use. In advanced stages it progresses to dementia and eventually death. The main symptoms are caused by massive loss of dopamine-secreting cells in the substantia nigra. These dopamine cells are especially vulnerable to damage. Dopamine has also been demonstrated to play a role in pain processing in multiple levels of the CNS including the spinal cord, cingulate cortex. Accordingly, decreased levels of dopamine have been associated with painful symptoms that frequently occur in Parkinson’s disease.

  • Endorphins – hormones that work with the endocrine system and released in our bodies. Endorphins can be found in the nervous system, the pituitary gland, or throughout other parts of the brain. Endorphins are hormones that allow the body to feel calm and relaxed. It is the body’s natural medication, which relieves tension and helps you sleep better. They are usually produced as a response to pain, fear or stress. Low endorphins level causes people to be anxious and more aware of pain. High endorphins level helps to diminish pain and have lesser effects towards stress, which is why foods such as chocolate produce a good feeling – they release endorphins.


  • Wikipedia pages for each bullet pointed hormone
  • Ahmad, H. R., & Brown, S. M. (2006). Serotonin. The American Journal of Psychiatry, Vol. 163(1), pp. 12.
  • Malick, J. B., & Bell, R. M. (1982). Endorphins: chemistry, physiology, pharmacology, and clinical relevance. New York.

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