Duckworth says prescribed medications are a major factor. If a patient is on anti-psychotics, for example, the medication can interfere with the body's ability to regulate temperature, leading to dehydration or heat stroke, he says.
"Heat is hard on human beings. Extreme temperatures are hard on human beings," Duckworth said. "The particular vulnerability is if you're taking psychiatric medicines, that can actually make the condition higher risk for you."
One example is Lithium, a drug used to treat bipolar disorder, which Duckworth says can increase the risk of dehydration, especially on hotter days.
Andrea Landry-Brown used to take Lithium and several other drugs to manage her post-traumatic stress disorder, bipolar disorder and anxiety. When she lived in California, the combination of heat and prescription medicines ramped up her symptoms in a way she'd never experienced before.
"I'm driving down the street and I literally saw people walking in front of my car," Landry-Brown says. As she stopped to wait for the people she saw to pass, her kids in the backseat told her to keep moving.
"I'm like, 'You don't see all [the] people in the street?' She says her kids responded, "'Mom, there's nobody there.'"