Low Libido: Which Blood Tests Should You Get?

Low libido (also called hypoactive sexual desire disorder when persistent and distressing) affects an estimated 1 in 3 women and 1 in 5 men at some point. It's commonly dismissed as "just stress" or a relationship issue — and sometimes it is — but persistent low libido that doesn't track with life circumstances frequently has identifiable medical contributors that respond to specific treatment.

The major medical contributors to low libido in both sexes:

• Low sex hormones — testosterone in men, but ALSO in women (women produce testosterone in smaller amounts, and it's critical for libido). Estradiol in women (declines in perimenopause/menopause); high estradiol in men can also suppress libido. DHEA-S contributes in both sexes.
• Elevated prolactin — suppresses sex hormones in both men and women. Common causes: medications (antipsychotics, some antidepressants, opioids, metoclopramide), severe stress, hypothyroidism, occasionally pituitary tumors (prolactinomas).
• Thyroid dysfunction — both hypothyroidism (low energy, low libido, depression) and hyperthyroidism (anxiety, sleep disruption affecting libido) cause sexual desire changes through multiple mechanisms.
• Insulin resistance / pre-diabetes — directly suppresses testosterone production in both sexes; the metabolic syndrome cluster (high blood sugar + abdominal obesity + low HDL) is strongly associated with low libido.
• Vitamin D deficiency — vitamin D receptors are present in tissues involved in hormone production; low vitamin D is associated with low testosterone and libido in observational studies.
• Medications — extensive list including SSRIs (very common), oral contraceptives, antihypertensives, finasteride, opioids, and many others. Don't stop medications independently; review with prescriber.
• Chronic stress and HPA-axis dysfunction — elevated cortisol suppresses sex hormones through multiple pathways.
• Sleep deprivation — even one week of restricted sleep significantly reduces testosterone in men; chronic poor sleep similarly affects women's hormones.

Many people with low libido have multiple contributing factors that compound — addressing them collectively often produces meaningful improvement.

Complete hormone profile. This is the foundation of any libido workup. Different markers matter more for men vs women, but the comprehensive profile catches the relevant patterns.

For men: Men's Hormone Panel ($159.99). Covers Total + Free Testosterone, SHBG, Estradiol, DHEA-S, Cortisol, Prolactin, and IGF-1. Key points:

• Total Testosterone — below 300 ng/dL on two morning draws is generally considered low.
• Free Testosterone — the bioavailable fraction. About 98% of testosterone is bound to SHBG and unavailable for use, so Total can look normal while Free is low if SHBG is elevated (which happens with age).
• Estradiol — yes, men need to test this. Elevated estradiol relative to testosterone causes mood changes, water retention, and suppressed libido. Reference range for men: 10-40 pg/mL.
• Morning draws (7-10 AM) are essential — testosterone peaks early and drops 30-50% by afternoon.

For women: Women's Hormone Panel ($159.99). Covers Estradiol, Progesterone, FSH, LH, Total + Free Testosterone, SHBG, DHEA-S, and Prolactin. Key points:

• Testosterone matters in women too — women produce testosterone in adrenal glands and ovaries, and low testosterone in women causes low libido, low energy, and decreased sense of well-being. Women's testosterone naturally declines from the 20s onward.
• Estradiol decline (perimenopause/menopause) — major libido contributor in women aged 40+. Estradiol affects vaginal lubrication, blood flow to genital tissues, and central nervous system effects on desire.
• If still cycling, test on days 2-5 for the cleanest baseline for FSH, LH, Estradiol.
• Day 21 of cycle for Progesterone (post-ovulatory peak).

Prolactin. Should be drawn at any time but not after recent sexual activity or vigorous exercise (both can transiently elevate prolactin). Normal ranges: 2-18 ng/mL for men, 4-29 ng/mL for women (higher during pregnancy/lactation). Elevation above 30-50 ng/mL warrants investigation; markedly elevated (above 100 ng/mL) requires pituitary MRI through endocrinology.

TSH + Free T4 (Thyroid). Both hyper- and hypothyroidism affect libido. TSH between 0.5-2.5 with Free T4 in the middle of normal range is optimal for sexual function.

Hemoglobin A1c + Fasting Insulin. Insulin resistance and pre-diabetes both suppress sex hormone production. Catching early (when fasting insulin is rising but A1c is still normal) gives the most reversible window.

Vitamin D, 25-Hydroxy. Optimal 40-60 ng/mL.

Medication-induced low libido is extremely common but often missed in standard medical care. If your low libido started or worsened after starting a new medication, that's a critical clue. Common offenders:

SSRIs (sertraline, fluoxetine, paroxetine, escitalopram, citalopram). Cause sexual dysfunction including low libido in 30-70% of users depending on the specific drug. Paroxetine has the highest rate; bupropion (a different class) has the lowest rate of sexual side effects and is sometimes a substitution option.

Hormonal birth control. Oral contraceptives, hormonal IUDs, and hormonal implants can suppress libido in some women through effects on free testosterone (oral contraceptives elevate SHBG, reducing free testosterone) and other mechanisms. Effects vary widely between individuals and specific formulations.

Antihypertensives. Beta-blockers and diuretics commonly cause sexual side effects in both men and women. ACE inhibitors and ARBs have fewer sexual side effects.

Finasteride and dutasteride. Used for hair loss and BPH; suppress DHT (a testosterone metabolite) and cause libido and erectile changes in a meaningful subset of users. Effects sometimes persist after stopping the medication (post-finasteride syndrome — controversial but recognized).

Opioids. Chronic opioid use suppresses testosterone production in both sexes (opioid-induced hypogonadism), commonly causing low libido as one of the most prominent symptoms.

Antihistamines (particularly first-generation like diphenhydramine, hydroxyzine). Anticholinergic effects can cause fatigue, brain fog, and sexual side effects.

What to do: Review all current medications with your prescriber. Don't stop medications independently — many require gradual taper. Often there's an alternative medication in the same class with fewer sexual side effects, or the dose can be adjusted, or the medication can be paused if appropriate. Bring the bloodwork results too — they help inform what alternatives might be best given your overall hormonal picture.

If testosterone is low (men) or in the lower portion of female range (women):

• Men: Confirm with second morning draw. If consistently low + symptoms, work with a urologist or men's-health specialist to evaluate TRT candidacy. Also address modifiable contributors — sleep, exercise, body composition, alcohol use, sleep apnea — which can sometimes restore testosterone without TRT.
• Women: Testosterone supplementation in women is more controversial and less standardized than in men. The Endocrine Society has guidelines for women with hypoactive sexual desire disorder, suggesting transdermal testosterone (off-label in US) at low doses for selected patients. NAMS-certified menopause practitioners are most likely to be knowledgeable about this.

If estradiol issue (women — declining in perimenopause/menopause): Hormone replacement therapy (HRT) is well-supported for symptomatic women within 10 years of menopause and meaningfully improves libido for many women. Vaginal estrogen specifically addresses genital tissue thinning, vaginal dryness, and discomfort with intercourse — frequently dramatically effective for postmenopausal women.

If prolactin elevated: Identify the cause. Medications are most common (review with prescriber). Moderate elevation often responds to addressing underlying cause. Markedly elevated (above 100 ng/mL) requires pituitary MRI through endocrinology to rule out prolactinoma.

If thyroid abnormal: Endocrinology or primary care. Treatment of thyroid dysfunction frequently restores libido over 3-6 months.

If metabolic markers abnormal: Lifestyle intervention is first-line. Addressing insulin resistance through diet, exercise, weight management, and sometimes metformin or GLP-1 medications can improve sex hormone production and libido.

If everything's normal: Consider non-medical contributors. Relationship counseling, sex therapy, addressing chronic stress, improving sleep quality, evaluating for sleep apnea. PDE5 inhibitors (for men with ED-related libido issues) can help — discuss with primary care or urology.

Specialists to consider:

• Urologist or men's-health specialist — for men with low testosterone and ED
• NAMS-certified menopause practitioner — for women in perimenopause/menopause (find at menopause.org)
• Reproductive endocrinologist or knowledgeable OB/GYN — for women with hormonal patterns suggesting PCOS or other endocrine issues
• Endocrinologist — for elevated prolactin, complex hormonal patterns, or suspected pituitary issues
• Sex therapist (certified through AASECT) — for the psychological and relationship components of low libido
• Sleep medicine — for suspected sleep apnea (very common cause of low libido in men particularly)