Low sexual desire (libido) is one of the most common issues people see their doctors about — but it’s often not discussed at all due to embarrassment. According to the Mayo Clinic and the Cleveland Clinic, it’s a multifactorial condition, and understanding its causes systematically is the first step in managing it. Statistically, according to the National Health and Social Life Survey, about 30-40% of adults experience a noticeable decrease in sexual desire at some point in their lives — meaning it’s not an exception, but a widespread, treatable condition.
Hormonal Causes Testosterone (in both sexes, though to varying degrees) directly contributes to low libido. In men, testosterone levels naturally decline with age—about 1% per year after age 30, a process sometimes called “andropause.” Clinically low levels are considered to be below 300 ng/dL, which can be determined with a simple blood test. In women, the sharp drop in estrogen and testosterone levels during menopause has a similar effect—often accompanied by vaginal dryness, which makes sex physically less pleasurable and reduces desire in additional, indirect ways. Thyroid dysfunction (hypothyroidism in particular) has also been linked to low libido, as thyroid hormones affect overall energy levels and metabolism. Elevated prolactin levels (hyperprolactinemia, often resulting from a benign pituitary tumor—prolactinoma—) are also a clinically proven cause in both sexes.
Psychological and emotional factors Depression is one of the most common causes — not only because of the condition itself, but also because one of the most common side effects of antidepressants (especially SSRI antidepressants) is decreased libido — studies have shown that 40-70% of people taking SSRIs experience some degree of sexual side effects. Chronic stress maintains high cortisol levels, which directly suppresses the production of reproductive hormones by affecting the hypothalamic-pituitary-gonadal axis — this makes evolutionary sense: the body is focused on survival, not reproduction, during times of stress. Self-esteem issues and body image concerns also play a role, especially during periods of weight gain or age-related changes.
Relationship Dynamics The natural decline in libido in long-term relationships is often part of a process of “desensitization”—the high dopamine levels caused by the novelty of a new partner gradually normalize over time, sometimes called “hedonic adaptation.” Unresolved conflicts, emotional distance, or a lack of time for each other (due to children, work, household chores)—all of these factors directly impact sexual desire. Sex therapists often note that couples with poor overall communication are equally likely to have low sexual satisfaction—and this is no coincidence.
Medications and chronic diseases In addition to antidepressants, libido is affected by certain groups of blood pressure medications (especially beta-blockers and thiazide diuretics), hormonal contraceptives in some women (because they reduce free testosterone levels in the blood), antihistamines in high doses, and chemotherapy. Chronic diseases — diabetes (which damages blood vessels and nerves, directly impairing blood flow to the genital area), cardiovascular disease, obesity (which alters the estrogen-testosterone balance due to the conversion of hormones in adipose tissue) — all of which directly or indirectly affect sexual function.
Lifestyle factors Sleep deprivation directly reduces testosterone levels — A 2011 study (University of Chicago) showed that a week of reduced sleep to 5 hours per night reduced testosterone levels in young men by 10-15%, an effect comparable to the natural decline in testosterone that occurs with 10-15 years of age. Excessive alcohol consumption, smoking (which damages the endothelium of blood vessels), and lack of physical activity also negatively affect blood circulation and hormonal balance. Obesity associated with a sedentary lifestyle further enhances this effect in a cyclical relationship.
Differences between men and women While many of the causes are common, the emphases differ. In men, decreased libido is more often directly related to testosterone levels and vascular health (along with erectile function). In women, research (including Rosemary Basson's Circular Model of Sexual Response) shows that emotional intimacy, relationship satisfaction, and contextual factors (stress, fatigue, body image) often play a more dominant role than purely hormonal indicators.
Diagnostic Process The initial visit to the doctor usually includes a detailed history (medications, sleep quality, stress levels, relationship status), blood tests (testosterone, thyroid hormones, prolactin, glucose), and a psychological evaluation as needed. It is important to remember that a single low testosterone result is not enough to make a diagnosis—repeated measurements are needed, as levels fluctuate throughout the day (highest in the morning).
When to see a doctor If decreased libido is sudden, long-lasting (more than 3 months), and causes distress to you personally or in your relationships, it is recommended to consult a doctor (therapist or endocrinologist) — checking your hormonal status with a blood test is often the first and most informative step. A professional evaluation, rather than self-diagnosis, allows you to accurately determine which factor (or combination of factors) is at play in a particular case — and therefore which approach (drug correction, therapy, lifestyle changes, or a combination of these) will be most effective.