Metro

Michelle Carter’s lawyer is partly blaming texts on her prescription. So what is Celexa?

Michelle Carter’s defense lawyer said in his opening statement that the tone of her text messages encouraging a friend to commit suicide was affected by the drug she was taking, Celexa.

What is Celexa? The drug, whose generic name is citalopram, is typically used to treat depression, according to webmd.com. It’s a type of drug known as a selective serotonin reuptake inhibitor.

Defense lawyer Joseph P. Cataldo said Carter was taking the drug for “impulse control issues,” among other conditions, and one of the known side effects of the drug is irritability that leads to “lashing out.” She had been hospitalized at least once before for mental problems, he said.

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Cataldo delivered his opening statement in Bristol Juvenile Court in Taunton where Carter is on trial for involuntary manslaughter in the death of Conrad Roy III in Fairhaven in 2014.

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The prosecution has pointed to a number of text messages sent by Carter to Roy, around the time he got into the cab of his truck, where he killed himself using carbon monoxide produced by fumes from a gas-powered water pump.

Carter, who was 17 years old at the time of Roy’s death, cajoles him to kill himself in the messages, prosecutors allege.

The federal PubMed Health website lists a wide range of possible side effects for Celexa, some specifically affecting younger people.

The drug “may cause some teenagers and young adults to be agitated, irritable, or display other abnormal behaviors. . . . Some people may have trouble sleeping, get upset easily, have a big increase in energy, or start to act reckless,” the site says.

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A medical study published in 2015 found that SSRI drugs might make some patients more likely to commit violent crimes. Carter, however, is only accused of persuading Roy to kill himself and was 30 miles away from the parking lot where Roy died.

Cataldo also said in his opening statement that Roy himself was troubled by mental health issues, was a victim of domestic violence who long wanted to end his life, and finally made the choice independent of everyone but himself on July 12, 2014.

“Conrad Roy was on this path to take his own life for years,’’ Cataldo said.

Jan Ransom of the Globe staff contributed to this report.