Overview.
Low libido affects up to 30% of women and 15% of men at some point. While sexual desire is complex—influenced by relationship, stress, and psychological factors—it's also hormone-dependent. Blood tests can identify treatable hormonal imbalances, particularly thyroid dysfunction, low testosterone, and prolactin abnormalities.
Low libido refers to persistently decreased interest in sexual activity that causes personal distress. It's different from occasional fluctuations, which are normal. In medical terms, it's categorized as 'hypoactive sexual desire disorder' when it causes significant distress. Both men and women can have hormone-driven causes.
Prevalence: Low libido is extremely common: affecting approximately 30% of women and 15% of men. Prevalence increases with age, particularly after menopause in women. It's one of the most common sexual health complaints in primary care.
What to test.
First-line tests
- Total Testosterone — Testosterone is the primary 'desire' hormone in both sexes. Low levels are a common, treatable cause of low libido.
- Free Testosterone — Free testosterone (the bioavailable fraction) may be low even when total testosterone is normal, especially if SHBG is elevated.
- TSH — Both hypothyroidism and hyperthyroidism affect libido. Thyroid dysfunction is common and easily treated.
- Prolactin — Elevated prolactin suppresses libido and can indicate a pituitary issue. Often overlooked but important to check.
Second-line tests
- SHBG — High SHBG binds testosterone, reducing free testosterone. Can explain low libido with 'normal' total testosterone.
- Estradiol — Low estrogen (menopause, over-exercise) causes vaginal dryness and decreased desire. High estrogen in men reduces libido.
- DHEA-S — DHEA is a precursor to sex hormones. Low levels may indicate adrenal insufficiency or aging-related decline.
- Fasting Glucose / HbA1c — Diabetes and prediabetes affect sexual function through nerve damage and vascular effects.
Specialized tests
- LH and FSH — Help distinguish primary (testicular/ovarian) from secondary (pituitary) hypogonadism if testosterone is low.
- Cortisol — Chronic stress and elevated cortisol suppress sex hormones. Consider if high stress is a factor.
- Progesterone (women) — Imbalanced progesterone relative to estrogen may affect libido, especially in perimenopause.
Common causes.
- Hypothyroidism — Low libido with fatigue, weight gain, depression, and cold intolerance
- Hyperthyroidism — Can cause low libido despite seeming 'high energy' due to anxiety and metabolic disruption
Diagnostic patterns.
- Low total and free testosterone + fatigue + decreased muscle mass — likely Hypogonadism (low testosterone). Next step: Check LH/FSH, consider testosterone replacement discussion
- Normal total testosterone but high SHBG + low free testosterone — likely SHBG-bound testosterone (functionally low). Next step: Address underlying cause of high SHBG, may need treatment
- Elevated prolactin + low testosterone + possibly galactorrhea — likely Hyperprolactinemia (possibly pituitary adenoma). Next step: MRI of pituitary, endocrinology referral
- Low libido + postmenopausal + vaginal dryness — likely Estrogen deficiency. Next step: Consider vaginal estrogen, systemic HRT discussion
Lifestyle.
Non-medical causes
- Relationship issues and partner dynamics
- Depression and anxiety
- Chronic stress and burnout
- Medication side effects (antidepressants, birth control, blood pressure meds)
- Poor body image and self-esteem
- Sleep deprivation
- Alcohol and substance use
- Normal aging (gradual decline is expected)
Considerations
- Address relationship and psychological factors first or concurrently
- Review all medications for sexual side effects
- Prioritize sleep (sex hormones are produced during sleep)
- Exercise regularly (improves hormone balance and body image)
- Reduce alcohol (depresses sexual function)
- Manage stress (cortisol suppresses sex hormones)
FAQs.
Can testosterone be low in women too?
Absolutely. Women produce testosterone (though less than men), and it's important for libido, energy, and mood. Testosterone peaks in a woman's 20s and declines with age. Low testosterone is a common and under-recognized cause of low libido in women.
Will testosterone replacement fix low libido?
If testosterone is truly low and that's the cause, replacement can help significantly. However, libido is complex—relationship factors, stress, and other hormones also matter. Testosterone isn't a guaranteed fix and has side effects to consider.
Can antidepressants cause low libido?
Yes—SSRIs (like Prozac, Zoloft) commonly cause sexual side effects including low desire, delayed orgasm, and erectile dysfunction. If this is an issue, discuss alternatives or additions with your prescriber.
Is low libido normal as I age?
Some decline is normal—testosterone drops about 1% per year after 30 in men, and estrogen/testosterone both decline after menopause in women. However, significant loss of desire that causes distress is worth investigating and treating.