A low sex drive rarely has a single cause. It typically results from a combination of hormonal shifts, stress, sleep habits, medications, and relationship dynamics working together. The good news is that most of these factors are identifiable and many are reversible. Understanding what’s behind the change is the first step toward addressing it.
How Hormones Affect Desire
Testosterone is the primary hormone driving sexual desire in both men and women. In adult men, normal levels range from about 193 to 824 ng/dL. In adult women, the range is much lower, under 40 ng/dL, but even small dips within that range can noticeably reduce interest in sex. Testosterone naturally declines with age in men, dropping roughly 1% per year after 30. When levels fall significantly below normal, low sex drive is one of the earliest and most common symptoms.
Thyroid problems also suppress desire through a less obvious pathway. When your thyroid is underactive (hypothyroidism), it triggers a rise in prolactin, a hormone best known for its role in breastfeeding. Elevated prolactin directly suppresses the hormonal chain that drives sexual desire by reducing the signals your brain sends to produce sex hormones. This is why people with untreated thyroid conditions often experience a drop in libido that seems unrelated to anything happening in their lives.
Menopause and Physical Changes
For women in midlife, low desire is strikingly common. A large Australian study of women aged 40 to 65 found that 69% reported low sexual desire. About one in three met the criteria for a clinical condition called hypoactive sexual desire disorder, where low desire persists for at least six months and causes significant personal distress.
The hormonal shifts of menopause drive much of this. Declining estrogen thins and dries vaginal tissue, a condition called vaginal atrophy, which can make sex uncomfortable or painful. Lower hormone levels also slow arousal, meaning it takes longer to feel physically ready. On top of that, night sweats disrupt sleep, leaving you fatigued and irritable. When sex starts to feel like a chore that might hurt, it’s completely logical for your brain to stop prioritizing it.
Medications That Lower Libido
Antidepressants are among the most common libido killers. SSRIs, the class that includes fluoxetine (Prozac), sertraline (Zoloft), and paroxetine (Paxil), cause sexual side effects in a large percentage of users. Estimates vary depending on how the question is asked, but studies have found rates ranging from 36% to as high as 73% for certain SSRIs. Paroxetine consistently ranks among the worst offenders, with sexual dysfunction rates between 43% and 71% across studies.
Other medications that commonly dampen desire include blood pressure drugs (especially beta-blockers), hormonal birth control, anti-seizure medications, and opioid painkillers. If your libido dropped around the same time you started a new medication, that timing is worth paying attention to. Switching to an alternative within the same drug class can sometimes resolve the problem without sacrificing the medication’s benefits.
Stress, Sleep, and the Cortisol Connection
Chronic stress suppresses sex drive through a measurable biological mechanism. When you’re stressed, your body produces cortisol, a hormone that works against the normal sexual response cycle. In healthy men, cortisol levels actually drop when sexual arousal begins, essentially clearing the way for the body to respond. In men with sexual dysfunction, researchers have found the opposite pattern: cortisol rises slightly during arousal instead of falling. Conditions like depression, obesity, diabetes, and heavy alcohol use can chronically elevate cortisol, creating a persistent hormonal environment that’s hostile to desire.
Sleep deprivation compounds the problem. A study at the University of Chicago found that restricting young, healthy men to five hours of sleep per night reduced their testosterone levels by 10% to 15%. The men also reported a noticeable decline in their overall sense of well-being. Since testosterone directly fuels desire, even a week or two of poor sleep can create a measurable dip in libido.
Nutritional Gaps That Matter
Zinc plays a surprisingly direct role in testosterone production. In one study, young men who ate a low-zinc diet for 20 weeks saw their testosterone levels drop by nearly 75%. When elderly men with low zinc levels received supplements, their testosterone nearly doubled. Zinc deficiency can also reduce your sense of smell, which research suggests is linked to libido, particularly in younger men. You can get zinc from oysters, red meat, poultry, beans, and nuts. If your diet is limited or heavily plant-based without supplementation, a deficiency is worth considering.
Relationship and Psychological Factors
Your brain is your most important sexual organ, and relationship stress, unresolved conflict, or emotional distance from a partner can shut down desire more effectively than any hormone imbalance. Loss of novelty in a long-term relationship is one of the most common and least discussed reasons people experience low libido. It doesn’t mean the relationship is failing. It means the effortless desire of early attraction has shifted into something that requires more intentional connection.
Body image, past trauma, performance anxiety, and depression all independently reduce desire. Depression is particularly tricky because the condition itself lowers libido, and the most commonly prescribed treatments (SSRIs) can lower it further. If you’re in this situation, it’s worth discussing alternatives or adjunct strategies with your prescriber rather than simply accepting it.
What a Medical Workup Looks Like
If low desire has persisted for several months and feels out of character, a medical evaluation can rule out treatable causes. For men, the standard starting panel includes morning testosterone levels measured on two separate days, thyroid function, prolactin, and sometimes estradiol to check hormone balance. If metabolic issues are suspected, blood sugar and inflammation markers may be added.
For women, the workup is similar but adjusted for menstrual cycle timing. Early in the cycle, a clinician may check estradiol, testosterone (using a sensitive test designed for lower female ranges), thyroid hormones, and DHEA-S, an adrenal hormone that contributes to sex drive. In both sexes, a protein called SHBG (sex hormone-binding globulin) is often measured because it binds to testosterone and can reduce the amount your body can actually use, even when total levels look normal on paper.
A clinical diagnosis of hypoactive sexual desire disorder requires that low desire has lasted at least six months and is causing you significant personal distress. That second criterion matters: if your sex drive is lower than it used to be but it doesn’t bother you, it’s not a disorder. The distress is part of the definition.
Practical Steps That Help
Prioritizing sleep is one of the fastest ways to support your hormonal environment. Aiming for seven to eight hours protects testosterone levels and reduces cortisol. Regular exercise, particularly strength training, has a well-documented effect on testosterone in both men and women, though excessive endurance training can temporarily suppress it.
Reducing alcohol intake helps on multiple fronts: it lowers cortisol, supports testosterone production, and improves sleep quality. Checking your zinc intake through diet or a simple supplement is a low-risk intervention with potential upside. For women in menopause, vaginal moisturizers and lubricants address the physical discomfort that can make desire feel pointless, and localized estrogen treatments can reverse vaginal atrophy without significant systemic hormone exposure.
If medications are the likely culprit, a conversation with your prescriber about timing adjustments, dose changes, or switching to an alternative with a better sexual side-effect profile can make a meaningful difference. Among antidepressants, bupropion is one that’s generally considered libido-neutral or even libido-positive compared to SSRIs.