A drop in libido is one of the most common health complaints, and it rarely has a single cause. Hormones, sleep, medications, stress, and underlying medical conditions can all suppress sexual desire, sometimes working together. Understanding which factors apply to you is the first step toward fixing the problem.
Hormones That Drive Sexual Desire
Testosterone is the primary hormone behind libido in both men and women. In men, levels below 300 ng/dL are clinically considered low, and roughly 68% of men in that range report decreased desire. But testosterone alone doesn’t tell the whole story. The ratio of testosterone to estrogen matters too. Men with a low testosterone-to-estrogen ratio are nearly four times more likely to experience reduced libido than men with a balanced ratio, even when their total testosterone isn’t dramatically low.
In women, testosterone also plays a role, though at much lower concentrations. Estrogen keeps vaginal tissue healthy and supports arousal, so drops during perimenopause, menopause, or while using certain hormonal contraceptives can dampen desire. Progesterone shifts during the menstrual cycle also influence how interested in sex you feel from week to week.
Medications That Suppress Desire
Antidepressants, especially SSRIs, are among the most common medication-related causes of low libido. Sexual side effects from these drugs are so widespread that they’re considered a defining drawback of the entire drug class. What’s less well known is that for some people, the sexual suppression persists even after stopping the medication. Australia’s Therapeutic Goods Administration has issued updated warnings about persistent sexual dysfunction after antidepressant use, noting these symptoms are likely underreported.
SSRIs aren’t the only culprits. Blood pressure medications (particularly older beta-blockers), hormonal birth control, anti-seizure drugs, opioid painkillers, and medications that block testosterone (sometimes prescribed for prostate conditions or hair loss) can all reduce desire. If your libido dropped noticeably after starting a new prescription, that timing is worth paying attention to.
Sleep, Stress, and Cortisol
Going a full 24 hours without sleep produces a measurable drop in testosterone. A meta-analysis of sleep deprivation studies found that total sleep deprivation of 24 hours or more significantly reduces testosterone levels, and 40 to 48 hours of lost sleep lowers them even further. Interestingly, partial sleep restriction over a few nights (sleeping five or six hours instead of eight) didn’t produce a statistically significant testosterone change in the same analysis. That said, chronic poor sleep raises cortisol, your body’s main stress hormone, and sustained high cortisol suppresses the hormones that fuel desire.
Stress works through the same pathway. When your body perceives ongoing threat, whether from work pressure, financial worry, or relationship conflict, it prioritizes survival over reproduction. Cortisol stays elevated, testosterone and estrogen production takes a back seat, and libido quietly fades. This isn’t a character flaw. It’s your endocrine system doing exactly what it evolved to do under pressure.
Thyroid Problems and Chronic Disease
Your thyroid sets the metabolic pace for nearly every system in your body, including your reproductive system. In a multicenter study of men with hypothyroidism (an underactive thyroid), 64% reported sexual dysfunction, including low desire. Thyroid issues are especially worth investigating because they’re common, treatable, and frequently missed. A simple blood test can identify them.
Diabetes creates a different problem. Sustained high blood sugar damages nerves and blood vessels over time, which directly affects sexual function. The Mayo Clinic notes that this vascular damage impairs blood flow and reduces the body’s production of nitric oxide, a chemical signal that’s essential for arousal in both men and women. High blood pressure and heart disease create similar vascular issues. If you have any of these conditions and notice your desire fading, the two are likely connected.
Iron Deficiency and Nutritional Gaps
Iron deficiency is an overlooked contributor, particularly in women. A 2023 review in Sexual Medicine Reviews found a significant linear relationship between iron levels and sexual function across multiple domains: desire, arousal, lubrication, orgasm, and satisfaction. Women with ferritin levels below 50 μg/L were less likely to enjoy intercourse or find their partner desirable compared to women with levels at or above that threshold.
The connection makes biological sense. Low iron causes fatigue, brain fog, anxiety, and depressed mood, all of which dampen the motivation to seek out intimacy. Iron deficiency may also promote avoidance behavior and blunted positive emotions, reducing the impulse to initiate social and sexual contact. You can be iron deficient without being formally anemic, so standard blood counts sometimes miss it. A ferritin test gives a more complete picture.
Postpartum and Breastfeeding
If you’ve recently had a baby, low libido is practically a biological guarantee. Prolactin, the hormone that drives milk production, actively suppresses sexual desire by counteracting dopamine, the brain chemical responsible for motivation, pleasure, and arousal. Prolactin levels peak about 30 to 45 minutes after a feeding begins, creating waves of suppression throughout the day for nursing mothers.
Sexual function typically stays suppressed for as long as breastfeeding continues. Many women report desire gradually returning during weaning, though the timeline varies. Add in sleep deprivation, physical recovery, and the psychological shift of new parenthood, and it would be surprising if libido weren’t affected.
Exercise: Too Little or Too Much
Regular physical activity generally supports healthy libido by improving circulation, reducing stress hormones, and boosting testosterone. But there’s a ceiling. Overtraining syndrome, which occurs when exercise intensity and volume outpace recovery, pushes the body into a chronic stress state. Cortisol rises, anabolic hormones like testosterone fall, and libido drops along with them. Other signs of overtraining include persistent fatigue, declining performance despite continued effort, mood changes, and trouble sleeping.
On the other end, a sedentary lifestyle contributes to weight gain, poor cardiovascular health, and lower testosterone, all of which reduce desire. Moderate, consistent exercise (strength training in particular) is one of the most reliable ways to support both hormonal health and sexual function.
Relationship and Psychological Factors
Biology doesn’t operate in a vacuum. Unresolved conflict with a partner, feeling emotionally disconnected, or carrying resentment can suppress desire even when your hormones are perfectly normal. Depression and anxiety are also major contributors. Depression in particular tends to flatten the reward circuitry in the brain, making activities that once felt pleasurable, including sex, feel neutral or unappealing.
Situational clues can help you sort psychological from physical causes. If you still experience desire in some contexts (during solo time, with a new fantasy, at certain points in your cycle) but not with your partner or in your usual routine, the issue is more likely psychological or relational. If desire has vanished across the board, a hormonal or medical cause becomes more probable. Both can coexist, and they often do.
Figuring Out Your Specific Cause
Start by looking at timing. Did your libido drop after starting a medication, entering a stressful period, having a baby, or gaining weight? A clear trigger narrows the search considerably. If nothing obvious stands out, a blood panel that includes testosterone, thyroid hormones, prolactin, and ferritin can identify or rule out the most common hormonal and nutritional causes.
Low libido that lasts more than a few months and causes distress is recognized as a clinical condition. The DSM-IV defined it as hypoactive sexual desire disorder, and while the DSM-5 restructured the diagnosis for women into a broader category called female sexual interest/arousal disorder, the core idea remains: persistent, distressing loss of desire that isn’t fully explained by another condition or a medication. That formal recognition means it’s taken seriously and there are established treatment paths, whether hormonal, psychological, or both.