Hormonal Contraception and Blood Tests: What Your Results May Not Be Telling You

Quick Facts

• Combined oral contraceptives (COCs) can significantly increase SHBG (sex hormone-binding globulin), suppressing free testosterone levels and altering how hormone tests should be interpreted.
• The pill can increase thyroid-binding proteins, meaning standard thyroid blood tests may appear abnormal despite normal thyroid function.
• Hormonal contraception has been associated with reductions in nutrients including B vitamins, magnesium, zinc, selenium, and folate.
• Some research has identified an association between hormonal contraception and mood changes in a subset of women, particularly adolescents.
• Blood test results taken during hormonal contraceptive use often reflect the pharmacological effects of contraception rather than true baseline physiology.
• These effects are rarely discussed during prescribing conversations and are not always considered when interpreting blood tests

 

 

For many women, hormonal contraception is safe, effective, and genuinely life-changing.

What is discussed far less often, however, is how hormonal contraception can alter blood test results, hormone binding proteins, nutrient status, and in some individuals, mood and wellbeing.

This does not mean hormonal contraception is “bad” or harmful for everyone. But it does mean that blood tests taken during hormonal contraceptive use often require significantly more context than most women are told.

A hormone result that appears low may not reflect true hormone production. A thyroid result that appears elevated may actually reflect increased binding proteins rather than thyroid disease. Fatigue, low mood, poor recovery, or low libido may sometimes have a measurable biochemical contribution that standard blood panels fail to identify.

Understanding how hormonal contraception affects blood chemistry allows blood test results to be interpreted more accurately and symptoms to be investigated more appropriately.

 

How Hormonal Contraception Works

 

Hormonal contraception works primarily by suppressing ovulation through effects on the hypothalamic-pituitary-ovarian (HPO) axis.

Combined oral contraceptives (COCs) contain both synthetic oestrogen and progestogen. These hormones suppress the luteinising hormone (LH) surge required for ovulation, preventing pregnancy.

 

Other hormonal contraceptive methods include:

• Progestogen-only pills
• Hormonal intrauterine systems (IUS/Mirena)
• Contraceptive injections
• Subdermal implants

 

Each method affects the body differently depending on:

• Hormonal composition
• Route of administration
• Degree of systemic absorption

The biochemical effects discussed throughout this article are most pronounced with combined oral contraceptives containing ethinylestradiol.

 

 

SHBG, Testosterone, and Why Hormone Results May Be Misleading

 

One of the most significant effects of combined oral contraceptives is the increase in sex hormone-binding globulin (SHBG).

SHBG is a protein produced by the liver that binds hormones such as testosterone and oestradiol in the bloodstream. Once bound, these hormones become biologically inactive.

Only Free Testosterone – the small unbound fraction  is available to tissues and cells.

 

How the Pill Affects SHBG

 

Research published in Clinical Chemistry and Laboratory Medicine found that SHBG levels increase by approximately 200% in combined oral contraceptive users.¹

This is clinically significant.

When SHBG rises substantially:

• More testosterone becomes bound
• Free testosterone falls
• Hormone panels may appear “low” despite normal production

 

A 2022 meta-analysis found that combined oral contraceptives reduced free testosterone by an average of 61%.²

This means many women testing hormones while on the pill will return suppressed free testosterone results that reflect contraceptive pharmacology rather than true baseline physiology.

 

Symptoms Associated With Low Free Testosterone

 

Some women may experience:

• Low libido
• Reduced motivation
• Fatigue
• Poor recovery
• Low mood
• Reduced exercise performance

while standard blood tests appear “within range”.

 

 

The Persistent SHBG Effect After Stopping the Pill

 

One of the least discussed aspects of hormonal contraception is that SHBG may remain elevated after stopping combined oral contraceptives.

Research published in the Journal of Sexual Medicine found SHBG levels remained significantly elevated in previous oral contraceptive users compared to women who had never used oral contraception.³

This means hormone testing performed shortly after stopping the pill may still not accurately reflect baseline hormone status.

For women investigating:

• Fatigue
• Low libido
• PCOS
• Androgen symptoms
• Fertility
• Hormone balance

Timing of testing matters significantly.

Most clinicians suggest waiting a minimum of three months after stopping combined oral contraceptives before interpreting hormone panels as representative of baseline physiology, though recovery timelines vary considerably between individuals.

 

 

Thyroid Blood Tests and Hormonal Contraception

 

Hormonal contraception can also alter thyroid blood test interpretation.

Combined oral contraceptives increase thyroxine-binding globulin (TBG), the protein responsible for transporting thyroid hormones through the bloodstream.

The same 2024 review found TBG increases by approximately 90% in combined oral contraceptive users.¹

 

 

Why This Matters:

 

When TBG rises:

• More thyroid hormone becomes protein-bound
• Total T4 and total T3 rise
• Standard thyroid panels may appear abnormal despite normal thyroid function

This is why Free T4 and Free T3 are often far more clinically useful than total thyroid hormones in women taking the pill.

Without this context, thyroid blood tests may:

• Appear falsely elevated
• Trigger unnecessary concern
• Lead to inaccurate interpretation

A 2025 study in the European Journal of Endocrinology confirmed oral oestrogen significantly increases SHBG, TBG, and cortisol-binding proteins compared to non-oral hormonal routes.⁴

 

 

Cortisol, Stress Hormones, and CBG

 

Combined oral contraceptives also increase corticosteroid-binding globulin (CBG), the primary transport protein for cortisol.

The 2024 review reported CBG elevations of approximately 100% in combined oral contraceptive users.¹

This means:

• Total serum cortisol may appear elevated
• Free cortisol may remain relatively unchanged
• Standard cortisol testing may not accurately reflect HPA axis function

 

This becomes particularly relevant when investigating symptoms such as:

• Chronic fatigue
• Burnout
• Stress-related symptoms
• Adrenal dysfunction concerns

 

Route of administration matters significantly here too, with oral oestrogen producing much greater binding protein changes than transdermal routes.

 

 

Nutrient Depletion and Hormonal Contraception

 

One of the most overlooked areas in women’s health is the effect of hormonal contraception on nutrient status.

Research has documented associations between hormonal contraception and reductions in:

• Folate
• Vitamin B6
• Vitamin B12
• Magnesium
• Zinc
• Selenium
• Vitamin C
• CoQ10

These effects appear to accumulate over time.⁵

 

Why Does This Happen?

 

Combined oral contraceptives affect:

• Hepatic (liver) enzyme activity
• Nutrient metabolism
• Nutrient excretion
• Absorption pathways

A systematic review found reductions in magnesium, zinc, selenium, and other nutrients were proportional to duration of contraceptive use.⁵

 

A UK review also identified interactions involving:

 

• B vitamins
• Magnesium
• Selenium
• Zinc
• Folate
• CoQ10
• Vitamin C

and recommended nutritional support be considered in women using combined oral contraceptives long-term.⁶

 

 

Common Nutrients Affected by the Pill

 

Folate (Vitamin B9)

Folate is essential for:

1. DNA synthesis
2. Methylation
3. Pregnancy health
4. Homocysteine regulation

Folate depletion becomes particularly important in women planning pregnancy after stopping contraception.

 

 

Pyridoxine (Vitamin B6)

 

Vitamin B6 supports:

1. Serotonin production
2. Dopamine synthesis
3. Nervous system regulation

 

Low levels may contribute to:

• Irritability
• Low mood
• Fatigue
• PMS-like symptoms

 

Cobalamin (Vitamin B12)

 

Low B12 may contribute to:

• Fatigue
  Cognitive symptoms
  Poor concentration
  Neuropathy
  Mood changes

 

Magnesium

 

Magnesium depletion may contribute to:

• Anxiety
• Poor sleep
• Muscle cramps
• Headaches
• Nervous system dysregulation

 

Zinc

 

Zinc plays important roles in:

• Immune function
• Skin health
• Neurotransmitter regulation
• Hormonal balance

 

Selenium

 

Selenium is essential for thyroid hormone conversion and antioxidant protection.

 

 

Hormonal Contraception and Mood

 

The relationship between hormonal contraception and mood is complex and highly individual.

Many women tolerate hormonal contraception well. Others report measurable changes in: mood, anxiety, emotional resilience, libido, motivation. The evidence in this area is substantial enough that informed discussions should include it.

What Does the Research Show?

 

A landmark Danish study involving over one million women found hormonal contraception users were 23% more likely to be prescribed antidepressants than non-users.⁷

 

The association was strongest:

• In adolescents
• During early contraceptive use
• In certain progestogen-only methods

A later UK Biobank cohort study involving over 260,000 women found increased depression rates during the first two years of combined oral contraceptive use, particularly in adolescents.⁸

A 2024 Frontiers in Psychology study also identified measurable depressive symptom changes in some oral contraceptive users.⁹

 

Importantly:

1. These studies show association, not universal causation.
2. Many women experience no mood effects.
3. Some women experience significant improvement in quality of life on hormonal contraception.

But the relationship is clinically relevant enough that it should not be dismissed.

 

 

The Nutritional Link to Mood

 

The overlap between nutrient depletion and mood symptoms is particularly important.

Several nutrients affected by hormonal contraception are directly involved in neurotransmitter production and nervous system regulation.

For example:

• B6 is required for serotonin and dopamine synthesis
• Magnesium regulates excitatory nervous system signalling
• Zinc influences BDNF and neuroplasticit
• Folate and B12 support methylation and neurotransmitter recycling

Whether nutrient optimisation improves pill-associated mood symptoms requires further research, but the mechanistic relationship is biologically plausible.

 

 

Injectable Contraceptives and Progestogen-Only Methods

 

The effects described throughout this article are most pronounced with combined oral contraceptives.

Other methods behave differently.

 

A 2024 randomised clinical trial found injectable contraceptives significantly reduced testosterone and SHBG through direct ovarian suppression mechanisms rather than SHBG elevation.¹⁰

 

Hormonal intrauterine systems (Mirena) generally produce:

• Lower systemic hormone exposure
• Smaller binding protein changes
• Less dramatic effects on hormone blood tests

This is why contraceptive type matters enormously when interpreting blood work.

 

 

What Blood Test Results Actually Reflect on the Pill

 

Several common blood tests may require contextual interpretation while using hormonal contraception.

Test	Common Effect on Combined Oral Contraceptives	What It May Actually Reflect
Free Testosterone	Often suppressed	Elevated SHBG rather than low production
SHBG	Significantly elevated	Pharmacological liver response to oestrogen
Total T4 / T3	Elevated	Increased TBG rather than thyroid overactivity
Total Cortisol	Elevated	Increased CBG rather than increased cortisol production
LH / FSH	Suppressed	Expected ovarian suppression
Oestradiol	Often low	Suppressed ovarian production; synthetic EE not measured
Vitamin D Binding Protein (DBP)	Elevated	Altered transport protein dynamics

 

 

When Should You Test Hormones After Stopping the Pill?

 

For women wanting a more accurate baseline hormone assessment, most clinicians recommend waiting at least:

• 3 months after stopping combined oral contraceptives
• Sometimes longer depending on SHBG recovery and symptom profile

 

Testing immediately after stopping may still reflect:

• Elevated binding proteins
• Suppressed ovarian signalling
• Altered hormone transport dynamics

There is no universally agreed timeframe because recovery varies substantially between individuals.

 

 

Frequently Asked Questions

 

 

Will my thyroid blood tests be accurate on the pill?

• Partially. Combined oral contraceptives increase thyroid-binding proteins, which can alter total thyroid hormone levels. Free T4 and Free T3 are usually more clinically useful.

 

 

Can the pill lower testosterone?

• Yes. Combined oral contraceptives suppress free testosterone through both SHBG elevation and ovarian suppression mechanisms.

 

 

Are all contraceptive methods the same?

 

• No.
• Combined oral contraceptives generally produce the largest changes in binding proteins and hormone interpretation. Hormonal coils and progestogen-only methods behave differently.

 

 

Should I take supplements while on hormonal contraception?

 

• Targeted testing is usually more useful than blindly supplementing. Nutritional support may be beneficial in some women, particularly if symptoms suggest depletion.

 

 

Does this mean hormonal contraception is harmful?

 

• No. Hormonal contraception is highly beneficial for many women.
• This article is about understanding how it affects physiology and blood test interpretation – not discouraging its use.

 

 

Final Thoughts

 

Hormonal contraception is effective, important, and for many women genuinely life-changing.

But it also produces measurable biochemical changes that affect:

• Hormone testing
• Thyroid interpretation
• Cortisol measurements
• Nutrient status
• Mood physiology

 

These effects are well documented within the scientific literature, yet they are rarely explained fully during prescribing conversations or considered during routine blood test interpretation.

The result is that many women are told their blood tests are “normal” when those results actually reflect the pharmacological effects of contraception rather than their underlying baseline physiology.

 

Understanding this context matters.

 

It allows symptoms to be investigated more accurately, blood tests to be interpreted more appropriately, and women to make more informed decisions about their health with a fuller understanding of what hormonal contraception may – and may not – be influencing.

 

 

REFERENCES

1. Louwers YV et al. The effect of hormonal contraceptive therapy on clinical laboratory parameters: a literature review. Clinical Chemistry and Laboratory Medicine. 2024.

2. Oral Contraceptive Effects on Testosterone Levels in Healthy Women: A Review. FACTS About Fertility. 2025.

3. Goldstat R et al. Impact of Oral Contraceptives on Sex Hormone-Binding Globulin and Androgen Levels in Women with Sexual Dysfunction. Journal of Sexual Medicine. 2006.

4. Stangl TA et al. The influence of gender-affirming hormone therapy on serum concentrations of hormone-binding proteins. European Journal of Endocrinology. 2025.

5. Palan P et al. Vitamin and mineral needs during oral contraceptive therapy: a systematic review. International Journal of Reproduction, Contraception, Obstetrics and Gynecology.

6. A Review of the Effects of Oral Contraceptives on Nutrient Status with Special Consideration to Folate in UK. Journal of Advances in Medicine and Medical Research. 2019.

7. Skovlund CW et al. Association of hormonal contraception with depression. JAMA Psychiatry. 2016;73(11):1154–1162.

8. Population-based cohort study of oral contraceptive use and risk of depression. Epidemiology and Psychiatric Sciences. 2023. PMC.

9. Mengelkoch S et al. Current oral contraceptive use affects explicit and implicit measures of depression in women. Frontiers in Psychology. 2024.

10. Avenant C et al. Injectable contraceptives DMPA and NET-EN substantially decrease testosterone and SHBG levels. PLOS ONE. 2024. PMC.