Key takeaways:
Hyoscyamine is a prescription medication that treats several gastrointestinal conditions. It works by blocking the chemical acetylcholine, which can cause several side effects.
Dry mouth, blurred vision, and constipation are some of the more common hyoscyamine side effects. They’re usually manageable with over-the-counter treatments.
More severe side effects include a fast heartbeat, heat intolerance, and confusion. Seek medical care if you experience these or other unusual or bothersome side effects after taking hyoscyamine.
Save on related medications
Hyoscyamine (Levsin, Anaspaz) is a medication that’s been around since the 1800s. Because it was developed before the FDA was created, it’s technically an unapproved drug. This means we don’t have the same safety information for hyoscyamine as we do for most FDA-approved medications.
Hyoscyamine is an anticholinergic medication. It blocks a chemical called acetylcholine (ACh) from working in the body. This can help treat a variety of symptoms, such as bladder spasms, irritable bowel syndrome, and stomach cramps. But blocking ACh can also cause several side effects.
Let’s review 10 hyoscyamine side effects and what you should do if you experience them.
1. Dry mouth
Hyoscyamine, like other anticholinergic medications, can cause dry mouth. Blocking ACh dries up the saliva in your mouth, which can be unpleasant.
In most cases, you can manage this side effect at home. Try chewing sugar-free gum or sipping water throughout the day. If that doesn’t help, there are several over-the-counter (OTC) dry mouth treatments. These include mouthwashes and saliva substitutes. Ask your pharmacist if you need help finding the right treatment for your needs.
If your dry mouth is severe or you’re having trouble swallowing normally, let your healthcare provider know. They may want to adjust your hyoscyamine dose or change your medication to manage this side effect.
2. Trouble urinating
ACh plays an important role in how your bladder works. When hyoscyamine blocks ACh, it may become difficult to urinate. You might have trouble peeing or feel like you can’t fully empty your bladder.
If you stop peeing completely or you have symptoms of an infection, such as a fever or pain in your abdomen, contact your healthcare provider right away. It can be dangerous if your bladder isn’t emptied regularly.
3. Constipation
Constipation is another common hyoscyamine side effect caused by the drug’s drying effect on the body.
There are many lifestyle changes that can help with constipation. Drinking plenty of water and exercising regularly are two examples. You can also try an OTC stool softener or laxative treatment with your healthcare provider’s approval.
Contact your provider if lifestyle changes and OTC medications don’t help. They may need to evaluate the cause of your constipation further. If at any point you have severe stomach pain or vomiting because of constipation, seek medical care right away.
4. Eye problems
Hyoscyamine can cause blurry vision and dry eyes. In rare cases, it can also cause a form of glaucoma
Hyoscyamine relaxes eye muscles, which can cause vision issues. Your pupils may also become dilated, which can make your eyes more sensitive to light.
As mentioned, hyoscyamine has a drying effect on your body. Dry eyes can cause pain or discomfort. Using OTC treatments for dry eyes, like artificial tears or ointments, may help.
If you’re having trouble seeing properly, let your healthcare provider know. In rare cases, hyoscyamine may cause a form of glaucoma called angle-closure glaucoma. This can lead to vision loss if left untreated. So if your vision becomes worse or you feel pain or pressure in your eye, seek medical care right away. If you already have glaucoma, talk to your healthcare provider before taking hyoscyamine — it may not be the right treatment for you.
5. Dizziness & drowsiness
You may feel dizzy or drowsy when taking hyoscyamine. This is a common side effect of medications that block ACh.
When you stand or sit up, move slowly to avoid dizziness. Until you know how hyoscyamine affects you, use caution when driving or participating in activities that require you to be alert and aware.
If these side effects continue or worsen, let your healthcare provider know. They may need to change your dose or the form of hyoscyamine you’re taking.
6. Headache
Hyoscyamine may cause headaches. Headaches are a common side effect of many medications. If you have headaches that don’t improve, OTC pain relievers like acetaminophen (Tylenol) or ibuprofen (Advil, Motrin) may help. But you should talk to your healthcare provider before taking OTC pain medications, to make sure they're a safe option for you.
If your headaches get worse or if they don’t go away, be sure to let your provider know. They may want to evaluate you further or might recommend stopping hyoscyamine.
7. Fast heart rate
You may notice that your heart rate speeds up when you’re taking hyoscyamine. This can be risky if you have heart problems or you’re over age 65.
Be sure to let your healthcare provider know if you have any heart conditions, including high blood pressure or irregular heart rhythms, before you start taking hyoscyamine. If you feel like your heart is racing or you have other symptoms that could be related to heart problems, like chest pain or trouble breathing, seek medical care right away.
8. Diarrhea
Unlike constipation, diarrhea isn’t a common hyoscyamine side effect. But it’s still possible.
If your diarrhea is severe or doesn’t go away, it could be a symptom of an intestinal obstruction. This happens when something is blocking food from moving through your intestines. Hyoscyamine can worsen intestinal obstructions. If you have diarrhea that doesn’t go away or other symptoms of an obstruction, like stomach pain or bloating, speak with your healthcare provider right away.
9. Flushing and heat intolerance
Your body sweats to help keep you cool in the heat. Hyoscyamine blocks your body’s ability to sweat. This can put you at a higher risk for heat exhaustion or heat stroke. Hyoscyamine can also cause your skin to become red and flushed more easily.
Be sure to limit your exposure to the sun and heat while taking hyoscyamine. When outdoors, wear loose clothing that protects you from the sun. Try to stay in the shade and drink plenty of water.
If you start to feel dizzy or tired, or if you notice your skin is red and clammy, it’s time to seek cooler temperatures. If you start feeling confused or lose consciousness, you’ll need medical care right away. If this becomes a regular problem, talk to your healthcare provider. Hyoscyamine may not be the best medication for you.
10. Confusion and short-term memory loss
In rare cases, hyoscyamine can have a negative effect on your brain, leading to confusion and short-term memory loss. More severe symptoms, such as hallucinations or agitation, are also possible. These symptoms are more common in older adults, and they usually go away within 48 hours of stopping hyoscyamine.
Contact your healthcare provider at the first sign of any mental side effects from hyoscyamine. They’ll likely want to change your medication to address this issue.
When should I contact my healthcare provider about hyoscyamine side effects?
It’s fine to contact your healthcare provider or pharmacist at any point if you’re finding a side effect bothersome. They may try changing your dose or the type of hyoscyamine you take.
If you have symptoms such as confusion, severe diarrhea, or chest or eye pain, seek emergency medical treatment. These are signs of more serious side effects that need care right away.
The bottom line
Hyoscyamine is an anticholinergic medication. It’s used to treat a variety of symptoms that can be caused by a number of medical conditions, including gastrointestinal and bladder-related conditions. But hyoscyamine can also cause side effects. Dry mouth, difficulty urinating, and blurred vision are common side effects. More serious side effects include a fast heart rate, intolerance to heat, and mental confusion.
You should contact your healthcare provider if you experience side effects from hyoscyamine. Some of the side effects you can manage at home. But several may require an adjustment to your medication.
Why trust our experts?
References
Ahmad, R., et al. (2021). The ocular adverse effects of oral drugs. Australian Prescriber.
DailyMed. (2022). Hyoscyamine sulfate.
Feinberg, M.,et al. (1993). The problems of anticholinergic adverse effects in older patients. Drugs & Aging.
Lieberman, J. A. (2004). Managing anticholinergic side effects. Primary Care Companion to The Journal of Clinical Psychiatry.
MedlinePlus. (2017). Hyoscyamine.
National Institute of Diabetes and Digestive and Kidney Diseases. (n.d.). Urinary retention.
PubChem. (2022). Hyoscyamine.
Sam, C., et al. (2022). Physiology, acetylcholine. StatPearls.
