Serotonin and dopamine pharmacology
Serotonin (5-HT) and dopamine receptor families, and the antidepressants, antiemetics, migraine, antipsychotic and Parkinson drugs that act on them.
Serotonin and dopamine are monoamines with many receptor subtypes spread across the brain, gut and blood vessels. One transmitter, many receptors: that is why drugs that act on a single subtype can treat very different conditions, and why broad drugs have broad side effects.
Serotonin receptors and their drugs
Serotonin is made from tryptophan. Because it does not cross the blood–brain barrier, brain and body pools are separate.
- 5-HT1A: partial agonist buspirone for anxiety
- 5-HT1B/1D: triptans narrow cranial vessels and calm trigeminal nerve endings in migraine
- 5-HT2A: blocked by second-generation antipsychotics; stimulated by hallucinogens
- 5-HT2B: chronic stimulation by some ergot-derived drugs is linked to heart valve fibrosis
- 5-HT3: ion channel in the gut and vomiting centre; ondansetron and other «-setrons» block it
- 5-HT4: prokinetic target in the gut
Raising serotonin: transporters and enzymes
SSRIs block the serotonin transporter (SERT); SNRIs also block the noradrenaline transporter; MAO inhibitors slow breakdown. Platelets take up serotonin through the same transporter, which is one reason SSRIs add to bleeding risk with anticoagulants or NSAIDs. Serotonin syndrome shows as mental change (agitation, confusion), autonomic signs (fever, sweating, fast heart rate) and neuromuscular signs (tremor, clonus, rigidity); it is a reason to check every serotonergic drug a patient takes.
Dopamine pathways and receptors
Dopamine is made from tyrosine via levodopa. The nigrostriatal pathway controls movement, the mesolimbic and mesocortical pathways carry reward and motivation, and the tuberoinfundibular pathway inhibits prolactin release from the pituitary. The chemoreceptor trigger zone in the area postrema, outside the full blood–brain barrier, uses D2 receptors to trigger vomiting.
Drugs that act on dopamine
The common link is the D2 receptor: drugs that block it can cause parkinsonism, acute dystonia, akathisia and, with long use, tardive dyskinesia (metoclopramide carries this warning); drugs that stimulate it can cause nausea, hallucinations and impulse-control problems.
- Raise dopamine signalling: levodopa with carbidopa, dopamine agonists (pramipexole, ropinirole), MAO-B and COMT inhibitors (Parkinson disease)
- Dopamine agonists such as cabergoline also suppress prolactin (prolactinoma)
- Block D2: antipsychotics (haloperidol, risperidone) and antiemetics (metoclopramide, prochlorperazine)
- Partial agonist: aripiprazole lowers dopamine signalling where it is high and raises it where it is low
Test yourself
Think of the answer, then tap the question to see it.
Which serotonin receptor is an ion channel, and which drugs block it?
5-HT3; ondansetron and the other «-setron» antiemetics block it.
Why can metoclopramide cause movement disorders?
It blocks dopamine D2 receptors, including those of the nigrostriatal movement pathway, and long use can cause tardive dyskinesia.
What are three features of serotonin syndrome?
Any three of: agitation or confusion, fever, sweating, fast heart rate, tremor, clonus, muscle rigidity.
Why does cabergoline lower prolactin?
It stimulates D2 receptors on pituitary lactotroph cells, copying dopamine's normal brake on prolactin release.
Example drugs
- Fluoxetine
- Sertraline
- Ondansetron
- Buspirone
- Sumatriptan
- Haloperidol
- Clozapine
- Aripiprazole
- Metoclopramide
- Cabergoline
- Levodopa + carbidopa
- Linezolid
Connections
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Serotonin syndrome: MedlinePlus Medical Encyclopedia (MedlinePlus (U.S. National Library of Medicine), 2026); Metoclopramide: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026).
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Representative model, for educational purposes only.