Scientists Debate Possible Viagra-Aggression Link
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SCIENTISTS DEBATE POSSIBLE VIAGRA-AGGRESSION LINK
By Todd Zwillich
Friday, December 6, 2002
WASHINGTON (Reuters Health) - A debate has begun among scientists about
whether Pfizer Inc.'s impotence drug Viagra (sildenafil) can be linked to
aggressive behavior and sexual violence.
One researcher has concluded that doctors should begin warning Viagra users
about the possibility of psychological and emotional side effects.
But other scientists, as well as officials at Pfizer, reject the claim as
In July of this year, Dr. Harold A. Milman, a toxicologist based in
Rockville, Maryland, published a report in the Annals of Pharmacotherapy
examining more than 12,000 reports of adverse events in men who took Viagra.
More than 270 of the reports, collected and archived by the US Food and Drug
Administration (FDA), detailed psychological side effects, including
dizziness, disorientation and amnesia. The drug was also listed as a suspect
in 22 reports involving aggression, 13 involving rape and 6 involving
murder, according to Milman's article.
FDA officials said that they have no plans to change Viagra's labeling in
light of Milman's report. But one top agency official said that the study
was important to scientific debate about the drug.
"(The report) had a lot of information that hadn't been pulled together in
one place before," Dr. Bernard Schwetz, FDA's senior advisor for science,
said in an interview.
Milman acknowledged that the adverse-event reports are anecdotal evidence.
"But it's clear that these men are behaving abnormally," he told Reuters
The theory that the drug may cause aggression has formed the basis of the
so-called "Viagra defense," a claim made by half a dozen defendants since
1998 that the drug caused them to commit violent crimes. Milman was hired as
an expert witness in one such case.
The Viagra defense has not been successful so far, but an Israeli court did
mention in a 1999 ruling against a rapist that the drug had played a role in
Viagra causes erections by working directly on the blood vessels of the
penis, not through actions in the brain. Clinical studies in more than 8,000
men showed that the drug caused central nervous system effects in less than
2% of users, none of whom became violent or disoriented, according to
"I'm not saying Viagra causes anything, but there is evidence to suggest an
association," said Milman, who noted that he is not an expert in Viagra's
biological mechanisms. Milman spent 18 years as a senior advisor at the US
Environmental Protection Agency and 10 as a cancer-drug expert at the
National Institutes of Health.
Scientists don't consider adverse-event reports to be hard evidence of a
causal link between a drug and an event. The reports don't always show which
other drugs patients were taking or note their state of health when taking
"You could take any product and connect individuals who use it with certain
behaviors. I think it's a coincidence," said Geoff Cook, a Pfizer spokesman.
"We don't think there is any credible medical evidence linking Viagra with
violent or aggressive behavior."
Still, adverse-event reports are often used as a way to flag side effects in
the general population that may have been missed during clinical studies.
Effects that fail to show up in several thousand test subjects have a better
chance of being noticed when millions of people have taken a drug.
Milman cited research in his report showing that sildenafil can enter the
brain and that the drug could affect biological pathways in parts of the
brain controlling sexual responses and aggression.
In interviews, other scientists rejected Milman's claims about a link to
aggressive behavior. "To me, it is an extremely remote hypothesis," said Dr.
Raymond C. Rosen, a professor of psychiatry and medicine at the University
of Medicine and Dentistry of New Jersey.
Rosen and Northwestern University toxicologist Dr. Kevin E. McKenna wrote to
the Annals of Pharmacotherapy this month challenging Milman's article.
Rosen told Reuters Health that there is no clinical evidence in humans that
the biological pathways affected by Viagra can cause aggression or violence.
He said that no patient he has ever evaluated has shown such symptoms.
"Changing anything clinically or legally because of this is stretching the
point totally beyond credibility," said Rosen, who is recognized as a
leading expert in sexual dysfunction. He noted that he has served in the
past as a paid consultant for Pfizer.
McKenna acknowledged that sildenafil could affect parts of the brain that
control sexual behavior, including the hypothalamus and parts of the
medulla. But studies in mice show that the drug would probably make
aggression less likely, not more likely, he said.
Milman said his paper was intended to encourage more scientists to look
directly at whether Viagra can cause problems. "There are a lot of question
marks," he said.
On that point, McKenna agreed. "I still believe behavioral effects of
sildenafil should be studied more closely," he said.
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