From Academic Kids

Missing image
Chemical structure of paroxetine


-4-(4-fluorophenyl)-piperidine hydrochloride

CAS number
ATC code
Chemical formula C19H20F1NO3, Cl, 0.5 H2O
Molecular weight 374.8
Bioavailability  ?
Max concentration  ? hours
Metabolism  ?
Elimination half-life 16-24 days
Excretion 66% urina
37% bile
Pregnancy category  ?
Legal status  ?
Routes of administration Oral

Paroxetine (paroxetine hydrochloride; trade names Paxil® (United States), Seroxat® (UK), Aropax® (Australia)) is an antidepressant of the selective serotonin reuptake inhibitor (SSRI) type. It was released onto the market in 1992 by the pharmaceutical company GlaxoSmithKline and has since become one of the most prescribed antidepressants on the market. It is the second most prescribed anti-depressant in the UK. It is now the subject of a fraud case in the United States due to allegations that GlaxoSmithKline suppressed research indicating that the drug caused young people to become suicidal.

Like some other antidepressants, it is also prescribed in the treatment of anxiety disorders and OCD. It was the first (and as of 2002, the only) antidepressant formally approved in the United States for the treatment of social anxiety disorder, causing it to be sometimes referred to (although inaccurately) as an anti-shyness drug.


Addiction Potential

The manufacturers claim it is impossible to become addicted to paroxetine. Other campaigners disagree. The medical community generally considers that withdrawal symptoms are not enough to regard a drug as addictive; it has to leave the user needing more and more in order to gain the same desired effect. Despite the frequency of 'Prozac poop-out', where an antidepressant becomes less effective over time, and that tolerance to side-effects over the first few weeks of treatment is acknowledged, it is still often claimed that tolerance does not occur. Note, however, that addiction is generally also an extremely debated issue, although no drug is generally considered to be addictive that does not have both withdrawal symptoms and tolerance.

Suicide and Children

Recent studies have found that the drug is relatively ineffective in children, and that they are prone to becoming suicidal in the early stages of treatment. Some psychologists believe that this is due to the way the drug begins to work in many patients. The first effect most people notice is a decrease in the lethargy and amotivation they experienced during their depression. This effect happens before the depression itself improves, so many children end up with enough "energy" and motivation to act on suicidal tendencies they may have already had. It is also important to note many people who are prescribed Paxil are suicidal to begin with, however most studies have compared suicide rates in patients using Paroxetine vs. a control group of depressed individuals not being treated with paroxetine.

Side Effects

A growing body of anecdotal evidence has raised concerns about some of its side effects.

Although the manufacturers say there is no reliable clinical evidence that the drug can cause violence or aggression, the company was sued in the US after Donald Schell killed his wife, daughter and grandchild after two days on the drug. During the investigation of the clinical records, it was reported that although paroxetine is safe and effective most of the time, in a minority of cases the drug can cause unpredictable side effects, such as wild mood swings or suicidal thoughts.

However, in June 2004 GlaxoSmithKline were again fighting a lawsuit over the drug due to allegations of fraud. The lawsuit alleges that five studies conducted by GSK between 1998 and 2002 suggested that the drug had little more effect than a placebo and increased suicidal tendencies.

Common side effects include:

  • drowsiness
  • sleepiness
  • nausea
  • upset stomach
  • dry mouth
  • constipation
  • diarrhea
  • decrease of sexual desire
  • delayed orgasm or anorgasmia
  • rash
  • itch
  • changes in urination

Individuals experiencing any of the following symptoms should contact their doctor immediately:

  • jaw, neck, and back muscle spasms
  • fever, chills, sore throat, or flu-like symptoms
  • yellowing of the skin or eyes

Withdrawal Symptoms

There is a growing amount of personal and anecdotal accounts of withdrawal symptoms from paroxetine. See, for example, [1] ( or [2] ( Initially, the response of drug regulators (based eg on a report by Price et al, 1995) were that withdrawal symptoms (or 'discontinuation reactions' as SKB/GSK insisted) were generally mild and short-lived, an opinion that has been replaced by mounting concern. Now, it seems about a third of users have problems stopping paroxetine, and the symptoms are strikingly similar ('electric shock' paraesthesia, dizziness, flu-like symptoms, etc) so that it is clear that what is under discussion is not psychological dependence.

Anyway a person taking paroxetine must not stop to take it at once. The best way to avoid any withdrawal symptoms is observing the simple strategy of gradually lowering the dose during several days.


Missing image
paroxetine structure

Paroxetine is chemically identified as (Immediate-Release Tablets / Oral Suspension:) (-)-trans-4R-(4-fluorophenyl)-3S-[(3,4-methylenedioxyphenoxy) methyl]piperidine hydrochloride hemihydrate, or (Controlled-Release Tablets:) (-)-(3S,4R)-4-[(p-fluorophenyl)-3-[(3,4-methylenedioxy)phenoxy]methyl] piperidine hydrochloride hemihydrate. Its empirical formula is C19H20FNO3, with a molecular weight of 374.8 (329.3703 as free base).

Paroxetine hydrochloride is an odorless, off-white powder, having a melting point range of 120 to 138C and a solubility of 5.4 mg/mL in water.


Paroxetine is a potent and selective serotonin (5-hydroxytryptamine, 5-HT) reuptake inhibitor (SSRI). This activity of the drug on brain neurons is thought to be responsible for its antidepressant effects.

Paroxetine is a phenylpiperidine derivative which is chemically unrelated to the tricyclic or tetracyclic antidepressants. In receptor binding studies, paroxetine did not exhibit significant affinity for the adrenergic (alpha(1), alpha(2), beta), dopaminergic, serotonergic (5HT(1), 5HT(2)), or histaminergic receptors of rat brain membrane. A weak affinity for the muscarinic acetylcholine receptor was evident. The predominant metabolites of paroxetine are essentially inactive as 5-HT reuptake inhibitors.

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