Testosterone therapy can cause infertility, and has been explored as a contraceptive

Various pollutants may be contributing to a male infertility crisis

Male infertility, due to declining sperm counts or quality, accounts for about half of the cases of infertility among couples. Recent research has found that global sperm counts fell, on average, by 1.2% per year between 1973 and 2018—from 104 million to 49 million per milliliter. From 2000, this rate of decline accelerated to more than 2.6% per year. (Some users may encounter a paywall.)

Testosterone prescriptions remain very low overall

Though demand for an injectable formulation of testosterone roughly doubled between 2019 and 2025, testosterone prescriptions still remain very uncommon—adding up to less than 2 per 100,000 prescriptions in 2025.

FDA removed its cardiovascular risk warning on testosterone products in 2025

The change came a decade after the FDA added the label. Recent work, including a gold-standard randomized trial, found that men receiving the products had similar cardiovascular risk levels as men taking placebo products. Testosterone, however, may hold other health risks, including infertility.

Estrogen is a really important hormone for men, too

Many people may be familiar with the idea that too much estrogen can cause infertility and other complications, including erectile dysfunction, but too little estrogen is also a significant medical concern because it can result in a reduced sex drive and limit overall growth.

Gender-affirming hormone therapy cues changes similar to puberty

When HRT is part of gender affirmation care, people receive regular doses of estrogen or testosterone to alter hormone levels to more closely align with those of cis individuals of that biological sex. HRT may affect voice pitch, body hair, bone density, and more. Many of those changes are not reversible with the cessation of therapy, though the effects may diminish.

Fertility treatments linked to increased risk of cancer among offspring

Recent research has explored potential links between increased childhood cancer occurrence, particularly leukemia, and assisted reproductive technology (ART). Though some studies have detected this type of association, researchers caution that it remains unclear if ART itself, fertility drugs, underlying infertility of the parents, or other unknown factors may explain any increased cancer numbers among ART-conceived children. Overall, the incidence of cancer in children, regardless of conception method, is very low.

Menopause hormone therapy infuses the body with estrogen after the body's natural levels drop

The treatments can treat symptoms like hot flashes and vaginal dryness at varying doses. Progestogen, another hormone, is also typically prescribed with estrogen because estrogen alone can thicken the uterus lining, which elevates the risk of developing endometrial cancer.

A new AI-assisted reproductive technique is finding 'hidden' sperm cells for those with very low sperm counts

Known as the Star system—for Sperm Track and Recovery—it uses artificial intelligence to help identify and locate "hidden" sperm in men with a rare infertility condition called azoospermia. The condition affects about 1% of men, and these individuals have sperm counts low enough that the individual spermatozoa in their ejaculate may be undetectable. In late 2025, the first baby was born after the child's parents used this assistive technique to locate sperm.

3-parent baby approach may help women with infertility

Though the topline promise of this approach is avoiding passing on mitochondrial diseases, some researchers and companies have been eyeing its potential for helping with female infertility, since faculty mitochondria may contribute to the condition. Recent research suggests this approach could be promising.

Treatment-induced menopause is menopause induced by surgery or medicine

Chemotherapy and radiation, as well as oophorectomy (a surgical procedure that removes the ovaries) and a radical hysterectomy can cause a woman to become menopausal. Women that go through medical menopause experience the same symptoms as women that experience menopause caused by natural hormonal cycles.

Follow an IVF procedure from lab to transplant

What happens once eggs are harvested from an ovary? How does an embryo form within a petri dish? This detailed video offers a glimpse of the transformations eggs experience as women age, and how sperm are injected into eggs in some forms of IVF treatment.

Find fertility clinics and their success rates in your state

This database from the Centers for Disease Control and Prevention provides a searchable portal of fertility clinics across the US, with reported data on services, total procedures performed, and live births recorded for as recently as 2022.

Immunosuppressants enable organ transplants, but come with severe side effects

This drug cocktail helps to lower your body's natural response to attack a transplanted organ. Such medications usually need to be taken for a lifetime after receiving an organ and can come with serious side effects including high blood pressure, diabetes, increased risk of some cancers, and high cholesterol, among others.

Supplements are only typically recommended for those with a proven deficiency

Blood tests and other dietary screening tools by clinicians and nutritionists can indicate whether someone is deficient in needed vitamins or minerals, and those results can then lead to a personalized care plan that may include supplements. Supplements can negatively interact with certain medications, so it's important to speak with your doctor about supplements before taking them.

Unlike milder fears, phobias may get in the way of proceeding with your life

Clinicians may recommend exposure therapy—exposing oneself to the thing triggering fears in some doses—as one way to help overcome a fear.

Doctors ignored women's pain as a nurse replaced their fentanyl with saline

This five-part podcast series, produced by Serial Productions, focuses on the experiences of women undergoing fertility treatments at a Yale clinic where a nurse secretly replaced pain medication with saline solution. This led to women experiencing excruciating pain during procedures, but the clinic downplayed or ignored their complaints.

Modern pregnancy tests detect a specific hormone in a woman's urine or blood

They pick up human chorionic gonadotropin, in either blood or urine. The hormone is produced by a woman's reproductive tissues during pregnancy.

Why physiology and genetics prevent king bees from existing

The mating process is fatal to male honey bees, as their endophallus detaches from their bodies and remains temporarily within the queen. Because fertilized honey bee eggs develop into female bees, if a male somehow did survive and become king, his line of succession would also abruptly end.

Indefinite cloning of some endangered species may not sustain their longevity because cloning success rates decrease as genetic mutations accumulate.

Why taking potassium iodide to protect against radioactivity is unlikely to be effective

Since the thyroid gland cannot distinguish between radioactive and non-radioactive iodine, taking potassium iodide pills causes the thyroid to absorb the medication, leaving it unable to take up radioactive iodine from the environment. However, while this protects the sensitive gland against the most prominent radioisotope produced in nuclear accidents, it does not protect other body parts or shield against other radioactive substances.

How depression affects the brain

Treatment for depression has historically hinged on the theory that the condition was caused by underactive or abnormal neurotransmitters, specifically serotonin and norepinephrine. This four-minute video by Yale Medicine details how these neurotransmitters didn't explain the symptoms of depression but, two other neurotransmitters involved in regulating mood and emotion did. GABA and glutamate, some of the brain's most plentiful neurotransmitters, may possibly be the source of depressive symptoms.

Has anyone had sex in space?

Reproduction is a basic human function, and while we've spent decades in space, no research has been done into the process. With many discussing the possibility of human-occupied bases on the moon, Mars, and more, understanding how sex works outside...

Fantasy sports can have adverse health effects

Experts warn that fantasy sports, including fantasy football, can encourage obsessive use because they offer hits of dopamine. Daily fantasy games, which function more like gambling, are especially problematic.

View the periodic table of radioactive elements, and a list of each's most stable isotopes

Technetium is the lightest artificial radioactive element, which is produced primarily as a byproduct of nuclear fission. Several unstable isotopes are commercially available to medical professionals and scientists, despite their radioactivity risks.

Type 1 diabetes is an inherent autoimmune disorder inhibiting insulin production

Diabetes causes the body to attack insulin-producing cells in the pancreas, causing a shortage or lack of insulin. This prevents the body from accessing and storing blood sugar—the brain and muscles' primary energy source. It's unclear what causes Type 1 diabetes, an incurable yet manageable chronic condition as of 2024.

Mifepristone, approved in 2000, is used to end early pregnancies

The drug works by blocking progesterone, a hormone that is needed to support pregnancy. Mifepristone is typically used in combination with a second drug, misoprostol, because this regimen often causes less cramping and bleeding than just using misoprostol alone.

Doctors differentiate between a phobia and fear by asking patients whether their fear interferes with their day-to-day activities.

Hookworm infection, though risky, may help fight certain autoimmune conditions by tamping down the immune system's inflammatory response.

The hormonal disorder PCOS was renamed PMOS in 2026, a move designed to improve care and research by shifting the focus to the hormonal causes of this condition that affects 1 in 8 women.

The syncytiotrophoblast is the outer layer of the placenta and the largest human cell, spanning an area about twice that of a king-sized bedsheet.

How fusion—which releases energy when two lighter atoms combine to form a heavier atom—differs from fission

While the first exchange-traded fund (a 'basket' of different assets that can be bought and sold on a stock exchange) in the US only launched in 1993, the global ETF market has grown to more than $10T in the short time since.

Studies suggest when you sleep is as important as how much you get, and syncing with your circadian rhythms may lead to less fatigue and improved long-term health outcomes

See the evolution of Ebola vaccine and treatment development.

Sunflowers have long been a symbol of nuclear disarmament because they can extract large amounts of radioactive cesium from soil.

The price of gas is a composite made up of several different factors, with the federal gas tax making up less than 20% of what drivers pay at the pump.

Alzheimer's can lead to brain shrinkage, with an average of around 2% of volume reduction per year

An investigation suggests a Scottish island became awash in forever chemicals via seafoam and seaspray—raising questions about what that means for the safety of other coastal areas.

The United States has had a tumultuous relationship with Cuba since its 1959 revolution, highlighted by a nuclear crisis and a decades-long trade embargo.

Iran's Revolutionary Guard Corps is independent of Iran's regular army and is one of the most powerful and influential military-political organizations in the Middle East.

Objects can be 3D printed with light by projecting 2D computerized tomography (CT) scans onto rotating cylinders of resin, which solidify upon exposure.

While the sun's gravity keeps the planets in orbit, their gravity also pulls on the sun, causing it and everything else in the solar system to orbit around a mutual balance point called the barycenter—the true center of the solar system.

NBA superstar Victor Wembanyama spent the 2025 summer training with monks in central China to enhance his body and mind.

Children are now three times more likely to say they want to be a YouTuber when they grow up than an astronaut, with some even attending 'YouTube camps' that teach kids how to create content for the platform.

Fireworks-related ER visits are on the rise—in 2024, they increased by 52% as compared to the prior year.

Take a 3D tour of the Hajj, Islam's annual pilgrimage to Mecca, undertaken by over 1.5 million Muslims.

Brandi Chastain, the star of the 1999 US victory over China in the 1999 Women's World Cup, was a last-second choice to take the penalty kick that sealed the victory.

20,000 letters to the advice columnist 'Dear Abby' provide insight into prevailing sex, religion, and LGBTQ fears, anxieties, and concerns from the 1950s onward.

To reduce wrinkles in clothing, research recommends gentle wash cycles with more water and tumble drying with smaller loads and longer times.

Pure water does not conduct electricity because this flow of energy requires the movement of charged particles, and water is a neutral molecule.