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A Kentucky man is invoking temporary insanity brought on by caffeine intoxication as his legal strategy to claim that he did not, as accused, murder his wife.

Prosecutors allege Woody Will Smith strangled his wife to death with an extension cord on May 4, 2009, according to the Kentucky Enquirer. Smith's lawyer claims that Smith, 33, became mentally unstable after weeks of downing sodas, energy drinks and caffeine-laced diet pills.

At the start of Smith's murder trial on today (Sept. 20), Smith's lawyer told the Newport, Ky., court that the high level of caffeine caused his client to become so mentally unstable that he couldn't have knowingly killed his wife.

This defense has been successfully used in court before, but does it make sense medically?

Caffeine-induced psychosis is not recognized by the Diagnostic and Statistical Manual of Mental Disorders (DSM), the reference book psychologists use when making diagnoses. However, the book does recognize caffeine intoxication, in which a person encounters ill-effects after ingesting 250 milligrams of caffeine (about two to three cups of brewed coffee) or more.

Hallucination more likely

The symptoms of caffeine intoxication listed in the DSM include rambling flows of thought and speech, cardiac arrhythmia, muscle twitching, gastrointestinal disturbance, insomnia, agitation (such as pacing around a room or wringing one's hands) and nervousness.

A 2009 study conducted by researchers at Durham University in England determined that people who ingest the caffeine equivalent of three cups of brewed coffee (or seven cups of instant coffee) are more likely to hallucinate. Heavy coffee drinkers had a three-times-higher tendency to hear voices and see things that were not there than those who consumed the equivalent of a half-cup of brewed coffee (or one cup of instant coffee).

Some negative, nervous reactions to caffeine, such as biting one's fingernails, may have an inherited explanation. People with certain genetic variations are more likely to bite their nails after drinking caffeine than those who don't, according to a 2002 study by University of Chicago researchers.

University of Chicago researchers also conducted a test in 2008 to see how much caffeine is needed to caffeine-induced anxiety, and found that while the highest dose used in their study (450 mg) increased anxiety in the majority of subjects.

Making matters worse

Behavioral or mental illnesses may make caffeine's effects even worse for some.

"Those with an underlying anxiety disorder may be more sensitive to the effects of caffeine," said Emma Childs of the University of Chicago, lead author of the 2008 study.

Childs told Life's Little Mysteries that while doses as high as 450 mg of caffeine caused some subjects to feel negative effects, including nausea, nervousness or jitteriness, the researchers saw no increases anger or hostility in the subjects during the study.

But the too-much-java defense has been used before, with some success.

Daniel Noble, then 31, blamed caffeine-induced psychosis for his hit-and-run accident at Washington State University, during which he broke the legs of two students.  Police subdued the 300-pound man with a stun gun after he resisted arrest and ran from the officers – while wearing only pajamas in 5-degree Fahrenheit (–15-degree Celsius) weather, according to ABC News.

A Whitman County, Wash., judge threw out the charges against Noble when it was found that he was suffering from undiagnosed bipolar disorder. However, the judge banned Noble from consuming any caffeinated products, according to news reports.

This article was provided by Life's Little Mysteries, a sister site to LiveScience.