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Sometimes medications that were developed to treat one condition can end up being useful for seemingly unrelated ailments.

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[ ♪ Intro ].

Modern medicine is pretty incredible. Walk into any drug store and you’ll see shelves of pills and syrups to treat your drippy nose, your rumbly stomach, or your aching back.

The pharmaceutical industry has poured billions of dollars into coming up with new treatments for everything from the common cold to cancer — but not every treatment is brand new. Medications that were developed to treat one condition can end up being useful for seemingly unrelated ailments, which actually involve similar parts of the body or brain. Here are 8 medications that turned out to do more than researchers initially thought.

First up is dextromethorphan. You might recognize it as the main ingredient in your favorite over-the-counter cough suppressant. This medication helps ease your hacking, but it doesn’t work like some cough medicines that loosen mucus in your windpipe.

Instead, dextromethorphan acts on your brain. It basically tells your lungs to chill out. It’s actually an opioid derivative, and we think it binds to and blocks a bunch of different neurotransmitter receptors, like NMDA and serotonin receptors.

That’s why it’s useful for treating other conditions. Dextromethorphan, combined with another chemical that keeps it from being broken down as quickly, is actually the only FDA-approved medication for treating pseudobulbar affect — where a person can’t control episodes of laughing or crying. It’s usually seen after a stroke or a brain injury or in neurodegenerative conditions.

In a healthy brain, there’s a careful balance between excitatory signaling and inhibitory signaling — telling cells to fire off a message or not to fire. Pseudobulbar affect is considered a disinhibition syndrome, meaning there’s less inhibitory signaling than normal. So the balance is off and there’s too much firing in the cells that control emotions.

Dextromethorphan is thought to help because it can block NMDA receptors, which reduces excitatory signaling and restores overall balance. This helps patients better control their emotional expressions, so when they get the giggles, it’s not because they literally can’t help it. Dextromethorphan isn’t the only drug that blocks NMDA receptors.

There’s also memantine, a drug that’s usually used to treat Alzheimer’s disease. Alzheimer’s is really complex, but scientists think that one of the big problems is something called glutamate toxicity. Glutamate is a neurotransmitter involved in excitatory signaling in the brain.

So when there’s too much excitatory signaling, a lot of extra glutamate ends up hanging around and binding to receptors. And over time, this overdose can kill neurons. So the logic behind memantine is that blocking NMDA receptors could reduce glutamate signaling and prevent that toxicity.

And it seems to work! Several review papers that looked at multiple studies showed that it can help with cognitive function and agitation in Alzheimer’s patients. But memantine might also help with other brain conditions, like obsessive compulsive disorder, or OCD.

OCD is fairly common — an estimated 1-3% of the U. S. population has it. But there aren’t too many medications to treat the symptoms.

These range from persistent anxiety-causing obsessions about things like germs, to feeling compelled to do certain repetitive actions, like turning the lights on and off. Recently, scientists have noticed that in both human and animal studies, changes in glutamate signaling in the brain seem to contribute to OCD symptoms. So they decided to try drugs that interact with NMDA receptors to balance things out.

And several clinical trials seem to show that memantine improves symptoms more than a placebo — which is good news for OCD patients who are struggling to find a treatment that works for them. Addictions can be hard to kick, but scientists have been working on medications like naltrexone that can help. It’s usually prescribed as part of addiction treatment for opioids, like heroin.

These drugs activate opioid receptors in the brain, which kicks off the biological processes that trigger feelings of pleasure and reward. Over time, repeated use of the drug can change signaling in the brain so that someone needs the drug to feel normal, and without the drug they can’t really function. And that’s when it becomes an addiction.

Naltrexone binds to opioid receptors, too — but instead of activating them, it blocks them. That way, it can keep addictive drugs from interacting with brain cells as much. It’s also prescribed to help with alcohol addiction, but it’s not totally clear how this works, since ethanol molecules don’t bind to opioid receptors.

One hypothesis is that when an addicted brain gets flooded with ethanol, it releases endorphins, which also activate the opioid system and could reinforce the behavior. And that’s what naltrexone might help stop. Now, naltrexone is also being used to treat behavioral addictions, like gambling or compulsive hair pulling.

This might not seem super surprising — after all, what works for one addiction should work for another, right? But think about it this way: when someone takes opioids or drinks alcohol, those substances get in their bloodstream and bind to receptors in their brain, leading to physical effects and contributing to addiction. Behavioral addictions don’t involve a substance.

They’re a result of how a particular behavior makes a person feel. So naltrexone seems to treat addiction whether there’s a physical substance or not. And that seems to suggest that endorphins or opioids binding to opioid receptors activate the same pathways.

And the more scientists understand about addiction and the brain pathways involved, the better we can treat it. The drug sildenafil was originally developed to treat problems like pulmonary hypertension. That’s where arteries and capillaries in the lungs and heart get constricted, making it harder for blood to flow properly.

So the heart has to work harder to pump, which can make it weaker over time. Specifically, sildenafil blocks the activity of an enzyme called phosphodiesterase type 5, or PDE5. PDE5 breaks down another compound that’s involved in relaxing smooth muscles — the ones that surround blood vessels and some organs like the intestines.

So when PDE5 is active, those muscles contract and blood vessels get narrower. And blocking the enzyme lets them relax, leading to more blood flow. During the testing phase of sildenafil, scientists noticed that it not only affected blood vessels in the lungs — it also affected blood vessels in the penis, because PDE5 is really active there too.

And this meant a bonus side effect: long-lasting erections. As a result of this … perk, the pharmaceutical company rebranded the drug as an erectile dysfunction medication and continued research. So sildenafil is now well known as Viagra.

There are other hypertension drugs with useful side effects, too. Like spironolactone, which was developed for treating high blood pressure and heart failure. This medicine blocks the binding of aldosterone, a hormone secreted by the adrenal glands right above your kidneys.

Aldosterone tells kidney cells to reabsorb sodium so you don’t pee it out, which helps keep your body’s salt levels balanced. And all those salts are pretty important. They keep your nerves firing, your muscles functioning, and your fluids balanced — so your cells stay nice and plump without getting too swollen.

But when there’s too much aldosterone, too much sodium gets absorbed back into the bloodstream. That, in turn, makes more water get reabsorbed, which means there’s a lot more fluid packed into your blood vessels — causing high blood pressure. So when spironolactone binds to and blocks these receptors, aldosterone can’t do as much, and blood pressure goes down.

But then doctors noticed that spironolactone also blocks progesterone and androgen receptors, which opened the door to new possible uses — like treating hormonal acne. Blocking androgen receptors means androgen hormones can’t bind. And this can lead to perks like less sebum — that oily gunk that protects your skin from drying out, but causes zits if there’s too much of it.

But because it blocks androgen hormones like testosterone, it can have side effects in biosex males — including gynecomastia, which is the growth of male breast tissue, and reduced fertility. In fact, spironolactone is so effective at blocking androgens that it can be prescribed along with estrogen for trans women who choose to undergo hormone therapy. Propranolol is another drug used to treat hypertension — but in a different way.

It’s a beta blocker, named because they block beta-adrenergic receptors, which are mostly found in organs like the heart and kidneys. Propranolol keeps chemicals like epinephrine and norepinephrine from binding — which you might know by a different name: adrenaline and noradrenaline. These compounds kick your body into gear, getting your heart to pump faster, dilating your pupils, and making you more alert.

All that “adrenaline rush” stuff. So the main effect of a beta blocker on the heart is to make it beat slower, lowering blood pressure. But research seems to show that propranolol might also help with certain kinds of anxiety — though it’s not totally clear how it works, and the data is spotty.

It could be because propranolol reduces the physiological sensations of high stress — like the sweaty palms and fast breathing that are also caused by epinephrine signaling. Without those sensations, anxiety levels in the brain might not spike as much, which could be enough to show some confidence before a speech or an important interview. And the list of hypertension medications with useful side effects doesn’t stop there!

A drug called minoxidil was developed to open potassium channels in smooth muscle cells, like the ones that line blood vessels. Opening these channels lets potassium ions flow through, which sets off a chain reaction that ultimately causes the muscle cells to relax. And this leads to wider blood vessels and lower blood pressure.

But one of the side effects of minoxidil is hypertrichosis, which is a fancy way of saying a lot of hair growth. So it’s also a great hair loss treatment. You’ve probably even heard of it before — as the brand name Rogaine.

What’s going on molecularly is a bit of a mystery. But some researchers think that because minoxidil can cause more blood flow, this provides more nutrients to the hair follicles and can encourage new cell growth. What we do know is that minoxidil seems to shorten the length of telogen, the resting phase of the hair growth cycle.

See, every strand of your hair isn’t always growing. Hair follicles chill in telogen for a few months before kicking back into anagen, the growing phase where new hairs are formed. So by shortening telogen and jump starting anagen, minoxidil can encourage new hair to grow before it would have on its own.

And that’s not the only medication that surprisingly affects hair. Bimatoprost is a drug that’s usually prescribed to treat glaucoma. Glaucoma is condition where a buildup of fluid increases the pressure inside someone’s eye, to the point of damaging the optic nerve.

If it’s not treated, it can lead to loss of sight and even total blindness. Bimatoprost is a synthetic prostaglandin, a hormone-like chemical found throughout the body that helps the eye drain extra fluid, getting the pressure closer to normal. It’s not totally clear how bimatoprost interacts with certain eye tissue to activate pathways involved in drainage, but it seems to work.

And it comes in an eyedropper form, making it easy for patients to use. But once again, doctors noticed a weird side effect: patients using bimatoprost found that their eyelashes were growing longer than normal. And after some more research, it’s officially FDA-approved for cosmetic use, and marketed as Latisse.

It’s not entirely clear how bimatoprost encourages eyelash growth, either. But it seems like it encourages eyelash follicles to jump back into the anagen phase prematurely, like minoxidil. And it even seems to stimulate melanin production in pigment-producing cells, which leads to longer, darker, fuller eyelashes.

All of these medications were initially developed with one goal in mind, but we learned a lot from studying all of their effects. These discoveries give doctors and patients more options for treating medical conditions… and for fixing their cosmetic woes. So we can’t really knock a treatment until we’ve tried it — with peer-reviewed clinical trials, of course.

Thanks for watching this episode of SciShow, which is produced by Complexly — a group of people who believe the more we understand about ourselves and the world, the better. If you want to learn more about human health and medicine, check out one of our other channels,. Healthcare Triage, at [ ♪ Outro ].