Hormones: dopamine is not the pleasure chemical, and the serotonin theory is poorly supported

Talk about hormones tends to begin and end with nicknames: dopamine is pleasure, serotonin is happiness, oxytocin is love, cortisol is stress. This article starts by asking how far those hold.

1. First, hormones and neurotransmitters are different

• A hormone is released by a gland and travels in the bloodstream to a distant target. Cortisol, insulin and oestrogen work this way.
• A neurotransmitter acts in the synaptic gap between neurons. Dopamine and serotonin belong mainly here.

The boundary is not absolute — both also act hormonally elsewhere in the body. But “happiness hormones” is a convenience phrase, not a physiological category.

2. Dopamine is not the pleasure chemical

The most widespread misunderstanding. Dopamine relates to wanting more than liking, and to prediction error.

The key observation: the dopamine signal rises when a reward is better than expected, and does not rise when it is exactly as expected. When it is worse, the signal drops. What dopamine carries is not the size of the pleasure but how far things departed from expectation.

So dopamine is less the substance that makes you feel good than the one that makes you move toward something. Blocking dopamine in rats leaves the reaction to sweetness intact while reducing the effort to obtain it — an observation that supports the distinction.

3. “Depression is caused by low serotonin” is poorly supported

A long-standing account holds that depression arises from a shortage of serotonin in the brain, and that this is why SSRIs work. That chemical-imbalance theory is judged to rest on weak evidence.

An umbrella review published in 2022 synthesised the several lines of evidence linking serotonin to depression and reported no consistent evidence that lowered serotonin activity or concentration causes depression.

One caution. This is not the claim that antidepressants do not work. How a drug works and whether it works are different questions. Do not use this paragraph as grounds to stop treatment — changes to medication belong with the prescribing clinician.

4. Oxytocin is not simply the love hormone either

Oxytocin relates to bonding and trust, but whom the bond is with moves along with it. Studies have found it heightening attachment to an in-group while also strengthening wariness of, or favouritism against, an out-group.

Oxytocin is thus less a substance that increases love than one that sharpens social boundaries.

5. A “dopamine detox” does not lower dopamine

A popular practice: cut off stimulation for a few days to “reset” dopamine receptors.

The phrase borrows neuroscience vocabulary, but there is no evidence it lowers dopamine levels or resets receptors. Dopamine is constantly needed for movement, motivation and learning; it is not something to abstain from.

That said, the practice is not meaningless. Reducing short, intense stimulation — infinite scroll, notifications — does restore attention and the tolerance for boredom. The effect is real; what explains it is not a dopamine reset but a rearrangement of habit and attention.

6. Principles for reading

• Accounts that pair one molecule with one emotion are almost always wrong. The same molecule does different work by region and context.
• Be wary of claims that a blood level explains your mood. What happens inside the brain is not well captured by a blood test.
• If changes in mood, sleep or appetite persist, see a clinician before reaching for a hormonal explanation.

References

Wolfram Schultz (1998) Predictive reward signal of dopamine neurons, Journal of Neurophysiology 80(1) — dopamine signalling reward prediction error.

Kent C. Berridge & Terry E. Robinson (1998) What is the role of dopamine in reward: hedonic impact, reward learning, or incentive salience?, Brain Research Reviews 28(3) — the distinction between liking and wanting.

Joanna Moncrieff et al. (2022) The serotonin theory of depression: a systematic umbrella review of the evidence, Molecular Psychiatry 28 — the assessment of the serotonin theory.

Carsten K. W. De Dreu et al. (2011) Oxytocin promotes human ethnocentrism, PNAS 108(4) — oxytocin strengthening in-group favouritism.