NSABP P-1: Tamoxifen for Breast Cancer Prevention
Journal of the National Cancer Institute (1998)
Reduced invasive breast cancer incidence by 49% in high-risk women, first chemoprevention agent for breast cancer.
How it works
Marek's Guided Optimization® Program combines advanced lab testing, a dedicated health coach and medical provider, and a personalized treatment plan, all built around your data.
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The process
1
Start your assessment
Complete your 45-min intake assessment
2
Get your labs drawn
4,000 partnered lab locations nationwide
3
Review with your coach
Screen-by-screen lab review
4
Receive your protocol
Treatment delivered to your door
Why Marek
The only program pairing you with a dedicated health coach and medical provider, built on precision diagnostics, with no subscription required.
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Meet our co-founder
Derek
Co-Founder · MPMD Podcast
"Over time, I found it incredibly difficult to get medical oversight for myself and my family that reflected the latest research, and that was preventative. That's why I started Marek Health."
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What we test
Every client's lab panel is hand-selected from 1,000+ available biomarkers, built around their specific goals.
Panel categories
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Treatments
700+ medical provider-prescribed therapies built from your labs. Browse by category or explore the full formulary.
Tamoxifen
Oral tablet (20mg)Available in all 50 statesMarketing purposes only. Actual medications, if prescribed, are dispensed by a licensed pharmacy.
hormones
TamoxifenTamoxifen
First-generation SERM, cornerstone treatment for HR+ breast cancer. In men, used for gynecomastia and as fertility-preserving adjunct to TRT by stimulating LH/FSH through hypothalamic estrogen receptor antagonism.
Reduces breast cancer recurrence by 40 to 50%
Raises testosterone in men via hypothalamic SERM effect
Preserves spermatogenesis
Preserves bone in premenopausal women
No commitment · HSA/FSA eligibleNo commitment · HSA/FSA eligible
How it works
Mechanism of action
Active metabolite endoxifen (via CYP2D6) competes at estrogen receptors. Antagonist in breast; partial agonist in bone, endometrium, and liver. Blocks negative estrogen feedback in hypothalamus, increasing GnRH, LH, FSH, and testosterone in men.
The baseline panel.
Every Marek client receives this baseline panel before a provider review. Your provider may add additional biomarkers based on your health history, symptoms, and goals, pulling from 1,000+ available markers. See more biomarkers →
Hormone Profile
12 markers
Sex hormones
- Total TestosteroneLC/MS
- Free TestosteroneEquilibrium Dialysis
- Estradiol, Sensitive / UltrasensitiveLC/MS
- Sex Hormone Binding Globulin (SHBG)
- ProgesteroneLC/MSFemale panel
- Prolactin
- Luteinizing Hormone (LH)
- Follicle-Stimulating Hormone (FSH)
- hCG, Total, QuantitativeFemale panel, pre-menopause
Adrenals & neurosteroids
- Cortisol
- DHEA-S
Growth hormone / IGF-1
- Insulin-Like Growth Factor I (IGF-1)
Thyroid Status
3 markers
Thyroid hormones
- Thyroid Stimulating Hormone (TSH)
- Free T4
- Free T3
Heart Health
9 markers
Cardiovascular health
- Total Cholesterol
- HDL Cholesterol
- LDL Cholesterol
- LDL:HDL Ratio
- VLDL Cholesterol
- Triglycerides
- Apolipoprotein-B (ApoB)
- C-Reactive Protein, High Sensitivity (hsCRP)
- Lipoprotein(a) (Lp(a))
Metabolism
3 markers
Insulin sensitivity
- Blood Glucose
- Fasting Insulin
- HbA1c
Organ Function
26 markers
Liver & pancreas
- AST
- ALT
- Bilirubin, Total
- γ-Glutamyl Transferase (GGT)
Kidney function
- BUN
- Creatinine w/ eGFR
Comprehensive Metabolic Panel (CMP)
- Glucose
- Blood Urea Nitrogen (BUN)
- Creatinine
- eGFR
- BUN/Creatinine Ratio
- Sodium
- Potassium
- Chloride
- Carbon Dioxide, Total
- Calcium
- Protein, Total
- Albumin
- Globulin, Total
- Albumin/Globulin (A/G) Ratio
- Alkaline Phosphatase (ALP)
- AST
- ALT
Prostate health
- Prostate-Specific Antigen (PSA)Male panel
- Free PSAMale panel
- % Free PSAMale panel
Nutrient Status
31 markers
Vitamins & minerals
- Vitamin D, 25-OHD (25-Hydroxy)
- Magnesium, RBC
Iron status
- Iron
- Iron Saturation
- TIBC
- UIBC
- Ferritin
Complete Blood Count (CBC)
- White Blood Count (WBC)
- Red Blood Count (RBC)
- Hemoglobin (Hgb)
- Hematocrit (HCT)
- MCV
- MCH
- MCHC
- Red Cell Distribution Width (RDW)
- Platelets
- Neutrophils
- Neutrophils (Absolute)
- Lymphocytes
- Lymphocytes (Absolute)
- Neutrophil/Lymphocyte Ratio
- Monocytes
- Monocytes (Absolute)
- Eosinophils
- Eosinophils (Absolute)
- Basophils
- Basophils (Absolute)
- Immature Cells
- Immature Granulocytes
- Immature Granulocytes (Absolute)
- NRBC, w/ Reflex for Immature Cells
Clinical evidence
The research behind Tamoxifen.
Safety profile
Monitoring & safety information.
Commonly reported side effects
- Hot flashes
- Vaginal dryness
- Mood changes
- Weight gain
Less common but serious risks
- Endometrial cancer (2 to 3x risk in women)
- VTE (2 to 3x risk)
- Stroke
- Drug interaction with CYP2D6 inhibitors (SSRIs)
Generally not appropriate for
- History of VTE (relative)
- Pregnancy
- Concurrent strong CYP2D6 inhibitors
Typical monitoring
- Annual gynecological exam (women)
- Ophthalmologic exam (long-term)
- Lipid panel
- Liver function
- Testosterone, LH/FSH, estradiol (men)
FAQ
Quick answers.
First-generation SERM, cornerstone treatment for HR+ breast cancer. In men, used for gynecomastia and as fertility-preserving adjunct to TRT by stimulating LH/FSH through hypothalamic estrogen receptor antagonism.
Reduces breast cancer recurrence by 40 to 50%. Raises testosterone in men via hypothalamic SERM effect. Preserves spermatogenesis. Preserves bone in premenopausal women.
Common side effects include: hot flashes, vaginal dryness, mood changes, weight gain. Most side effects are dose-dependent and may resolve with continued use or dose adjustment.
First-generation SERM, cornerstone treatment for HR+ breast cancer. In men, used for gynecomastia and as fertility-preserving adjunct to TRT by stimulating LH/FSH through hypothalamic estrogen receptor antagonism.
Treatments are dependent on licensed clinical prescription. Client costs vary based on individual labs and panel in treatments and services.