For anyone, taking high doses of antihistamines could have cardiovascular effects like arrhythmias (when your heart beat becomes irregular), heart palpitations, syncope (losing consciousness and passing out), hypotension (lowering of your blood pressure), and even cardiac arrest.
If you mix sedatives, tranquilizers, or alcohol with large doses of antihistamine, you might increase or amplify some of the depressant effects of antihistamines (like drowsiness).
Take selective serotonin reuptake inhibitors (SSRIs), like sertraline (Zoloft) and paroxetine (Paxil). “When somebody is taking an SSRI, they have more serotonin in their system for longer, which can have a sedating effect,” leading to sleepiness.
On the other side of the spectrum, norepinephrine and dopamine reuptake inhibitors, like the popular drug bupropion (Wellbutrin), increase the levels of those two neurotransmitters in the brain.
Therefore, most health care providers encourage women who are pregnant or nursing not to use antihistamines.
This phenomenon likely centers around rapid eye movement (REM) sleep, the mentally restorative sleep cycle in which dreams occur. Escitalopram (Lexapro), sertraline (Zoloft), duloxetine (Cymbalta), and paroxetine (Paxil) have all been shown to have this effect.
When your REM sleep is suppressed, you might wake up more frequently, which then allows you to remember more dreams.
When you loop in drugs meant to combat depression, your sleep habits can change even more.
“It depends on the antidepressant—some can be alerting, while some can be sedating,” Breus says.“Generally speaking, these medications affect neurotransmitters like serotonin, dopamine, and norepinephrine,” which are important for regulating your emotions, board-certified sleep medicine doctor and neurologist W. D., of Charlottesville Neurology and Sleep Medicine and author of , tells SELF. “All of these chemicals are big players in the pathways of maintaining or initiating sleep, or chemicals that help you feel awake during the day,” Winter says.