SSRI stands for Selective Serotonin Reuptake Inhibitor. The word `selective' has special pharmacological meaning, and, in context, refers to the ability of a drug to inhibit the neural/glial uptake of serotonin, over, say, noradrenaline.

Serotonin is the trivial name for the molecule 5-hydroxytryptamine (5-HT). It has important and separate functions in the central nervous system (as a neurotransmitter) and in the cardiovascular system (as a hormone).

The SSRIs' antidepressant properties are attributed to their effects on serotonin uptake in the central nervous system*. The Custodian's assertion that Zoloft functions as an antidepressant by `blocking the reuptake of serotonin from the bloodstream into cells' is not believed to be the case*, and would appear merely to be a misunderstanding. The rest of The Custodian's article makes illuminating reading.

Halcyon&on has provided a learned write-up about serotonin from a biochemist's point of view -- it's not really light reading :-)


  • Rang, H. P. et al. Pharmacology; Churchill Livingstone: London, 3rd ed.; 1995, 590.

* Here's an excerpt from the manufacturer-supplied product information for sertraline: (Roerig)

The mechanism of action of sertraline is presumed to be linked to its inhibition of CNS neuronal uptake of serotonin (5HT). Studies at clinically relevant doses in humans have demonstrated that sertraline blocks the uptake of serotonin into human platelets. In vitro studies in animals also suggest that sertraline is a potent and selective inhibitor of neuronal serotonin reuptake and has only very weak effects on noradrenaline and dopamine neuronal reuptake.

Antidepressants Selective serotonin reuptake inhibitor (SSRI)
Whats the deal with SSRIs??

The SSRI drugs are used in treatment for depression and often in conjunction with psychotherapy. They decrease the reuptake of serotonin and, to a much lesser degree, other catecholamines, prolonging the action of serotonin and helping to stabilize mood.
The result is an elevated level of serotonin in the central nervous system (CNS) and may result in elevated mood and, consequently, reduced depression.

Citalopram / Celexa
Fluoxetine / Prozac
Fluvoxamine / Luvox
Paroxetine / Paxil
Sertraline / Zoloft
Escitalopram / Lexapro

Side Effects
Side effects for SSRI’s include: Anxiety, chills, mania, hypomania, seizures, tremors, hypotension, palpitations, hypoglycemia, unusual bleeding r/t platelet function, hyponatremia, dyspnea
As this drug raises levels of serotonin, other drugs that raise serotonin levels are contraindicated. These include: MAO inhibitors, amphetamines, other psychostimulants, and other antidepressants.
Serotonin syndrome
Serotonin syndrome is a rare but serious complication; it can be life threatening. It is the result of dangerously high levels of serotonin in the CNS. Symptoms include: agitation, confusion, diaphoresis, diarrhea, fever, hyperactive reflexes, poor coordination, restlessness, shaking, shivering, talking or acting with uncontrolled excitement, tremor, or twitching.
MAO inhibitors should be stopped for 14 days before beginning SSRI therapy, and SSRI therapy should be stopped for 14 days prior to starting MAO inhibitor therapy.

SSRIs are a class of drugs (including Prozac, Zoloft and Paxil) which are used as prescription antidepressants. Functionally, they increase the levels of serotonin in the body. These drugs can be dangerous if they're mixed with other drugs such as other antidepressants, illicit drugs (LSD, cocaine, methamphetamine), some antihistamines (Seldane, Histmanal), some antibiotics, and calcium channel blockers.

Side effects include lethargy, confusion, flushing, sweating and muscle spasms. Overdose can cause damage to red blood cells, breathing problems and kidney damage.

From the BioTech Dictionary at For further information see the BioTech homenode.

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