The study, published this week, by scientists in Norway, suggests the antidepressant was linked to an increased suicide risk in adults.
The drug manufacturer is arguing that the research was flawed and misleading.
This strongly worded statement, from Europe's biggest drugmaker, highlights industry sensitivity to drug safety issues, and comes after a Texas court awarded $253 million against Merck & Co. Inc. in a case over its painkiller Vioxx last week.
This is not the first time that GlaxoSmithKline's Paxil and other similar drugs have been linked to suicide and doctors around the world have been warned they should not generally be used among under-18s.
But now the researchers at Oslo University say that the drug also seemed to affect adults in the same way.
In their analysis of trials involving more than 1,500 patients they found seven suicide attempts among those taking the drug and only one among those taking a placebo.
According to GSK the analysis is misleading as it focuses on incorrectly selected data, collected 15 years ago when GSK was seeking approval for the medicine, which is also known as Seroxat and paroxetine.
The company says the study results only cause confusion and unnecessary concern for patients using an SSRI (selective serotonin reuptake inhibitor), such as paroxetine, for treatment of depression.
They say the sub-analysis also fails to acknowledge the current body of data, which is significantly more extensive and which has been recently reviewed by EU authorities.
Earlier this year experts at the European Medicines Agency reaffirmed the positive benefit-risk for Paxil in the treatment of adult anxiety and depression.
The study is published in the BMC Medicine open access journal.
"MAO-B inhibitors delay the need for levodopa by about six months in patients with early disease," says Counsell. "However, this is almost certainly because they have a mild symptomatic effect rather than fundamentally altering the progression of the disease. The question is whether this short delay is important."
"I suspect that selegiline delays motor fluctuations as it continuously delivers dopamine," says Irene Litvan, M.D. of the University of Louisville School of Medicine. "The unresolved question is if it is truly worthwhile prescribing MAO-B inhibitors. Perhaps rasagiline, another MAO-B inhibitor which is more potent, may have more of a future in treating [Parkinson's] as is offers additional benefits, for instance, as an antioxidant."
Rasagiline is newly licensed MAO-B inhibitor. "I would favor selegiline for further study because this is the most widely used; many would favor rasagiline because newer is often perceived as better," Counsell says.
In the United States, at least 500,000 people are believed to have Parkinson's disease, and about 50,000 new cases are reported annually, affecting about 1 percent to 2 percent of people over the age of 60 years. The chances of developing Parkinson's increase with advancing age. The early-onset form, which accounts for 5 percent to 10 percent of people with Parkinson's, occurs before age 50 (such as seen in actor Michael J. Fox, who was diagnosed in his 30s).
The main symptoms of Parkinson's are subtle and gradually worsen, and include trembling in hands, arms, legs, jaw and face; rigidity, or stiffness of the limbs and trunk; slowness of movement; and postural instability, impaired balance and coordination. As the disease progresses, patients may have difficulty walking, talking or completing other simple tasks. Depression and other emotional changes can also occur.