How your menstrual cycle may affect your response to brain stimulation

Estrogen and progesterone change across your menstrual cycle and influence brain signaling. Could those changes affect how your brain responds to stimulation?

Research and thousands of women who have used Samphire’s stimulation suggests it can, but evidence is still emerging.

Your brain responds to its biological environment

Researchers have long used gentle electrical stimulation to study and influence brain activity, delivering a weak current through electrodes on the scalp, to address symptoms.

Why might estrogen and progesterone affect the brain?

Estrogen and progesterone affect several systems involved in brain signaling. Estrogen has been linked with excitation and plasticity, the brain’s capacity to adapt. Progesterone and some of its metabolites can affect gamma-aminobutyric acid (GABA), one of the brain’s main inhibitory signaling systems.

Smith et al. (1999) used brain stimulation to study 13 healthy women during the follicular and luteal phases. They found greater inhibition during the luteal phase and suggested that changes in GABA signaling could help explain the finding.

Estrogen and electrical brain stimulation

Lee et al. (2018) studied 29 healthy adults, including 14 women. The women completed sessions during the early follicular phase, when estrogen was lower, and the mid-luteal phase, when estrogen was higher. They received 15 minutes of electrical brain stimulation over the left dorsolateral prefrontal cortex, an area involved in thinking and regulating emotions. The researchers found a different electroencephalogram (EEG) response, a measure of electrical brain activity, after stimulation in the higher-estrogen condition. They also measured estrogen in blood samples rather than relying on cycle timing alone.

The researchers used the same stimulation protocol in both hormonal conditions.

What about magnetic stimulation?

Chung et al. (2019) studied 29 healthy adults, including 14 women, using high-frequency repetitive brain stimulation over the left dorsolateral prefrontal cortex (same region that is stimulated with the Samphire Headband). The women completed sessions during higher- and lower-estrogen phases. The researchers found a broader brain response after stimulation in the higher-estrogen condition.

Does the menstrual phase matter?

Ramdeo et al. (2024) studied 29 women who completed real and sham intermittent theta-burst stimulation, a form of magnetic stimulation, during the follicular and luteal phases. After real stimulation, the researchers found an increase in a measure of motor-cortex response during the follicular phase, but not during the luteal or sham conditions. This suggests that the capacity for a short-term plastic response may vary across the menstrual cycle and depending on your symptoms and conditions.

Hormones aren't the whole story

Hormone levels vary between people and between cycles, so cycle phase cannot tell you someone’s exact hormonal state. Hormonal contraception and how researchers identify cycle phase also matter.

This is why studies that measure hormone levels directly can provide information that cycle timing alone cannot.

What the research can tell us

These small studies used different stimulation methods, brain regions, and outcome measures. They mostly measured brain activity rather than improvements in cognition, physical performance, or how people feel. They do not establish a universally better cycle phase for stimulation or show that changes in brain activity lead to better everyday outcomes.

However, Samphire’s clinical studies and user accounts indicate that correctly timing the phase of your cycle or hormonal changes to your symptoms and your brain stimulation patterns can lead to meaningful improvements in brain stimulation efficacy.

More research is needed to understand when differences in brain response translate into meaningful changes in everyday life.

Personalizing your brain stimulation

Your response to brain stimulation may vary with your biological context.

The Samphire app fully personalizes your brain stimulation protocol to your needs and cycle phase. It also accounts for perimenopause, irregular cycles such as those associated with polyendocrine metabolic ovarian syndrome (PMOS), previously known as polycystic ovary syndrome (PCOS), trying to conceive, and hormonal contraception.

The research above helps explain why cycle context may matter, although it does not establish that one phase is universally better for brain stimulation.

Explore how the Samphire app personalizes your brain stimulation protocol: https://apps.apple.com/gb/app/samphire/id6523432233