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Introducing TOM, an initiative launched in 2024 to understand how the menstrual cycle affects common medical test results.
Every person's cycle is unique, but that's exactly why we should improve our understanding of why it varies.
Consideration of cycle day in clinical assessments, drug trials and experimental design may hold key in improving patient outcomes and understanding of disease.
Sign up for TOM's PILOT 2026 today!
Rolling registration is open. Places for each cycle are allocated on a first-come first-served basis.
The objective of TOM's PILOT is to determine whether the timing of medical tests (i.e. blood tests, urine tests, scans) during the menstrual cycle influences their outcome. We want to promote the practice of documenting the cycle day for women of reproductive age.
Am I eligible?
You can participate if you:
• Are between 18-25 years old
• Have regular periods (every 24-38 days)
• Are not currently using hormonal birth control (pills, hormonal intra-uterine device (IUD), implant, injection, patch, or ring)
• Are not planning to become pregnant in the next 6 months
Time commitment
This fully remote study will use individual cycle length and test results input (i.e. blood tests) to explore the effects of the menstrual cycle in mainstream medical tests.
Expected time commitment is up to 30 minutes monthly, on the first day of your cycle, for 6 months (January-June 2026).
How we use your data
Data collected in the pilot will include medical test results and general demographic information.
You can request your data to be deleted at any time by sending an email to research@tomshealth.co.uk
Launching in 2026, we aim to recruit 100 people with regular menstrual cycles for a 6-month research project.
This pilot will build the foundation for integrating monthly cycle considerations into clinical practice, generating preliminary data and establishing protocols for larger-scale investigation of how hormonal variations impact medical testing and diagnosis.
Any questions? Please reach us via email at hello@tomshealth.co.uk
WHAT IS TOM?
The 'Time of the Month' (TOM) Project is uncovering a hidden truth: the drugs we take, the clinical trials we run, and the medical advice we follow have been designed as if the menstrual cycle doesn't exist. Our mission is to make the characterisation of menstrual cycle a priority for clinical researchers everywhere.
What is the menstrual cycle?
The menstrual cycle is a series of changes in production of hormones and body systems that occurs monthly to prepare the body for a possible pregnancy. The cycle is counted from the first day of one period to the first day of the next.
Bleeding can be light or heavy, painful or pain-free, and the cycle length can vary. Individuals can use period-tracking apps to understand what is typical for them. Yet, healthcare systems have not incorporated a personalised "normal" baseline to refer to.
The straightforward addition of "cycle day" to medical records can enrich the clinical literature by:
• Establishing precise reference "healthy/normal" ranges for medical tests, instead of assuming constant values throughout the month
• Enable researchers to incorporate cycle day/phase as a controlled variable in clinical trials, what is currently dismissed as "too complicated" to study
• Improving test timing to better detect health abnormalities, to reduce false-negative results when investigating underlying conditions
Why care?
The challenge of understanding the determinants of common diseases of people with uteruses is substantial, and is often a combination of genetic, environmental and lifestyle factors.
TOM will contribute to the study of:
-> drug dosing in all clinical trials, as hormonal changes affect how drugs are metabolised and the effects they cause
-> the effect of long-term contraception, as well as why certain people have side effects from them and not others
-> hidden markers of disease that disproportionately affect women i.e. dementia, endometriosis.
-> the mechanisms of pain, in the context of pre-menstrual syndrome (PMS) and endometriosis, as well as chronic pain
-> the effect of hormones in mood and the link between irregular cycles and higher levels of depression and anxiety
