Hormones are chemical signals that travel through your bloodstream and tell every organ what to do. When they're in sync you sleep well, feel steady, and your body hums. When they're not — even slightly — the ripple effects are felt everywhere. Select a hormone to explore exactly what it does, what knocks it off, and what the research says helps.
Estrogen is actually a family of three hormones: estradiol (E2, the main reproductive form), estrone (E1, dominant after menopause), and estriol (E3, made during pregnancy). Estradiol does most of the work across your reproductive years — it builds the uterine lining, triggers ovulation, maintains bone density, supports cardiovascular health, and has profound effects on mood and memory via receptors distributed throughout the brain. It interacts with 400+ physiological functions and is not a "vanity hormone" — it's a survival hormone. The gut microbiome even has a dedicated sub-community (the estrobolome) responsible for recycling estrogen through the body.
Ask for oestradiol (E2) on day 2–3 of your cycle. If peri/post-menopausal, any day. Always pair with SHBG — it affects how much estrogen is biologically active. For full metabolite mapping, consider the DUTCH test (dried urine), which reveals whether your estrogen detoxifies via the safer 2-OH or the concerning 16-OH pathway.
Progesterone is made by the corpus luteum — the shell left behind after an egg is released. If you don't ovulate, you don't make progesterone, regardless of whether you have a period. Beyond reproduction, progesterone converts to allopregnanolone, which activates GABA receptors — the same system benzodiazepines target. This is why ovulation supports sleep and calm. Low progesterone (often from anovulatory cycles) is the most underdiagnosed cause of anxiety, insomnia, and heavy periods in women in their 30s and 40s. Importantly, synthetic progestins in the Pill behave very differently — many are androgenic and do not carry progesterone's calming benefits.
Test serum progesterone on day 21 of a 28-day cycle (7 days before expected period in longer cycles). Above 30 nmol/L confirms ovulation. Below this suggests anovulation. Day 3 progesterone testing is always low and clinically meaningless — don't accept it as a substitute.
Women make testosterone too — and it matters enormously. Women produce about one-tenth of the male amount, but it's the main driver of libido, physical energy, muscle building, motivation, and cognitive sharpness. It's made in the ovaries and adrenals, and also converted from DHEA. Levels start declining from your late 20s. Crucially, testosterone is bound by SHBG (sex hormone-binding globulin) — making the free portion the biologically active part. The combined oral contraceptive pill raises SHBG by up to 3-fold, binding more testosterone and explaining post-Pill libido loss that can persist for months after stopping.
Ask for total testosterone + free testosterone + SHBG — total alone is almost meaningless without SHBG context. Add DHEAS to determine whether origin is ovarian or adrenal. Test in the morning (8–10am) — testosterone peaks shortly after waking. If PCOS is suspected, add LH, FSH, androstenedione.
Cortisol is your body's primary stress response hormone — but also an essential regulator of blood sugar, immune function, inflammation, and the sleep-wake cycle. It follows a strict 24-hour curve: it peaks 30–45 minutes after waking (the cortisol awakening response, or CAR) to provide morning energy, then gradually declines to its lowest point around midnight. Chronic stress flattens this curve — blunting the morning peak and elevating levels at night, causing the "tired but wired" syndrome. Women appear to have a more reactive HPA axis than men, and cortisol dysregulation is central to everything from weight gain to thyroid problems to infertility.
A single morning serum cortisol (8am fasting) gives a baseline — normal roughly 170–500 nmol/L. More informative: a 4-point salivary cortisol (morning, noon, evening, night) maps your full daily rhythm and identifies flat vs. high-flat patterns. The DUTCH test (dried urine) adds metabolised cortisol and the full sex hormone picture.
The thyroid gland produces T4 (thyroxine) and T3 (triiodothyronine) — hormones that regulate the metabolic rate of virtually every cell. The pituitary monitors levels and releases TSH to signal for more. Almost every function — heart rate, digestion, temperature, mood, hair growth, ovulation — depends on adequate thyroid hormone. The most common thyroid condition in women is Hashimoto's thyroiditis: an autoimmune attack on the thyroid that affects 1 in 8 women in their lifetime. Women are 7–10× more likely than men to develop it — yet it typically takes 5–7 years to diagnose because TSH-only testing misses it for years.
A standard test only checks TSH — this is insufficient. Request: TSH, Free T4, Free T3, TPO antibodies, AND thyroglobulin antibodies. TSH can remain "normal" for years while antibodies are rising and the thyroid is being destroyed. FT3 can be low even when TSH and FT4 look normal. Test fasting in the morning, before any thyroid medication.
Insulin is released by the pancreas after eating to help cells absorb glucose. Insulin resistance — where cells stop responding normally, requiring more and more insulin — is epidemic and deeply gendered. Women with PCOS have a unique form that persists even at normal weight. Beyond PCOS, insulin resistance is the central driver of type 2 diabetes, cardiovascular disease, and fatty liver. The hormonal implications are significant: high insulin directly stimulates the ovaries to produce more testosterone, disrupts ovulation, and drives estrogen dominance through increased aromatase activity — making it the nexus hormone connecting metabolic and reproductive health.
Standard panels miss insulin resistance. Ask for: fasting insulin (optimal <8 mIU/L), fasting glucose, then calculate HOMA-IR = (insulin × glucose) ÷ 22.5 — above 2.0 suggests resistance. Also request fasting triglycerides and the triglyceride:HDL ratio — above 1.7 is a sensitive proxy marker. For PCOS: request a 2-hour oral glucose tolerance test with insulin readings at 0, 1, and 2 hours.
Hormones don't work in isolation. Every imbalance creates a ripple through the whole system — which is why fixing one often requires understanding several.
Cortisol and progesterone compete for the same receptor. Chronic stress "drowns out" progesterone signals — you may have adequate progesterone but still experience deficiency symptoms. This is called pregnenolone steal. Stress management is non-negotiable for PMS.
High insulin directly stimulates ovarian theca cells to produce more testosterone — the central PCOS mechanism. Lowering insulin consistently reduces testosterone and restores ovulation, even without weight loss.
Estrogen normally downregulates cortisol responses. As estrogen declines in perimenopause, the stress system becomes hyperreactive — explaining why perimenopausal anxiety often feels qualitatively different and more disproportionate.
Cortisol inhibits T4→T3 conversion. High-stress states produce "T3 syndrome" — TSH and T4 look normal, but FT3 is low, causing hypothyroid-type fatigue and weight gain missed by TSH-only testing.
High estrogen raises thyroxine-binding globulin (TBG), binding more thyroid hormone and reducing the free, active portions. This is why some women feel worse on the combined pill or during pregnancy.
The oral contraceptive pill raises SHBG — binding testosterone and making it unavailable. Post-Pill SHBG elevation can persist 6+ months after stopping, keeping free testosterone low and libido suppressed.