THC Increases Heart Rate in Women Without Increasing Anxiety, Study Finds
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Larger THC doses increase the physical indicators of anxiety in women without necessarily elevating the feelings of anxiety, according to a new study from researchers at the University of Chicago.
The study authors also note the lack of a THC effect on the sympathetic autonomic response in these women, which directly contrasts with the previous studies done on men. This may indicate that there is a hormonal component to the effects of cannabis, the researchers say, which would underlie the need for further studies exploring cannabis’ unique effects on women.
THC can affect heart function
The autonomic nervous system is responsible for a wide array of unconscious actions; it keeps the heart beating, the lungs breathing, and the digestive system digesting.
This study examined the effect of THC on the autonomic system by measuring changes in heart rate and blood pressure, as well as taking several measures of sympathetic and parasympathetic cardiac control. Increased sympathetic cardiac control has previously been tied to feelings of anxiety and anger, whereas decreased parasympathetic control is associated with anxiety, negative mood, and emotional regulation.
Published in Psychophysiology, the study examined 37 healthy women who were occasional users of cannabis. Each study participant attended three experimental sessions, where they were blindly given either a placebo, a low dose, or a high dose of THC. In addition to the physical measurements of cardiac function, the participants also recorded their subjective experience through completing three questionnaires designed to assess overall drug effect, cannabis-specific sensations, and feelings of anxiety.
The researchers found that larger doses of THC increased the participants’ heart rate, while also decreasing high frequency heart rate variability (HF-HRV), which is a measure of parasympathetic activity. However, despite both these measures being physical indicators of anxiety, the women did not report any increase in their own subjective feelings of anxiety.
No significant changes were recorded in the pre-ejection period (PEP), the term given to the time between the electrical activation of the heart’s ventricles and the resulting opening of the aortic valve. PEP is a measure of cardiac sympathetic function and the lack of effect on PEP here is notable as other cannabis studies on men have found differences in sympathetic activity after THC administration.
Mismatch seen between physical and emotional sensations
The researchers say that this mismatch is curious, but not necessarily surprising.
“There are theories that people report anxiety when they have an increased sense of heart rate,” said de Wit. “When they feel their heart rate increasing, they will interpret that as anxiety.”
“[...] any drug can work in a variety of different ways,” de Wit continued. “The receptors and pathways that account for the psychological effects to THC might differ from the physiological. The mechanisms might be dissociated.”
The study participants did notice their raised heart rates, but, for whatever reason, did not self-associate this with feeling anxious. However, the researchers recognize that this might be different in cannabis users taking the drug in real-world conditions and not in a controlled laboratory environment.
“It’s important for us to understand what variables influence responses to drugs,” said de Wit.
Even if sex and sex hormones are found to not be a factor in the THC-anxiety response, de Wit says that this would still be an “important result from a scientific and safety point of view.”
The need for more female-focused cannabis research
Despite the long history that humans have with cannabis, there’s still much to learn about the plant and its effects on the body and mind. Additionally, what has been learned has largely been garnered from studies predominantly involving healthy, white, adult men.
Animal studies have shown that female rats are more sensitive to the effects of cannabis than males. Some early human investigations have also now found differences in how the sexes react to vaped cannabis, with women reporting more anxiety and restlessness than the men.
“Cannabis has been around for a long time, but it has not been well studied,” said senior study author Harriet de Wit, a professor in the Department of Psychiatry and Behavioral Neuroscience at the University of Chicago, in a statement.
“So much of what we believe is based on studies in males,” de Wit said. “A lot of knowledge may not hold true in females.”
This new study is part of a larger investigation by the de Wit lab into the interactions between THC and the menstrual cycle. With some preclinical studies finding links between THC and the ovarian hormone estradiol, the researchers want to see more study of cannabis at different points of the normal female menstrual cycle, as well as the potential effects on cisgender women taking hormonal birth control and transgender women taking estradiol as a part of hormone therapy.