Hyoscyamine: 7 things you should know

Medically reviewed by Carmen Pope, BPharm. Last updated on Nov 20, 2023.

1. How it works

• Hyoscyamine may be used to treat some gastrointestinal and genitourinary disorders and inhibit salivation and excessive secretions of the respiratory tract.
• Hyoscyamine works by inhibiting the action of acetylcholine, the main neurotransmitter of the parasympathetic nervous system. It decreases the motility of the gastrointestinal (GI) tract and reduces the secretion of acid from the stomach and other fluids from the gastrointestinal tract and airways. It may be used to relieve gastrointestinal cramps and excessive secretions.
• Hyoscyamine belongs to the class of medicines known as anticholinergics/antispasmodics.

2. Upsides

• May be used to treat bladder spasms, colic, diverticulitis, irritable bowel syndrome, pancreatitis, and peptic ulcer disease.
• Relieves spasms or cramping and controls excessive bronchial, pharyngeal, stomach, and tracheal secretions.
• Can decrease the incidence of rhinitis (a runny nose) and reduce excessive production of saliva.
• May be used as a premedication before anesthesia, endoscopy, or some imaging studies.
• May be considered in children over the age of six with urinary incontinence to help control urination.
• Occasionally, may be considered for certain heart conditions or to help control the symptoms of Parkinson's disease.
• May be used as an antidote to cholinesterase inhibitor toxicity.
• When given in conjunction with a cholinesterase reactivator (pralidoxime chloride), hyoscyamine can reverse muscarinic effects associated with toxic exposure to organophosphate pesticides and other anticholinesterase compounds, although atropine may be preferred.
• Twice as potent as atropine, therefore, a lower dosage can be used to provide a similar effect with less potential for adverse reactions.
• Hyoscyamine is administered orally. Hyoscyamine sulfate may be administered orally, sublingually, or by IM or IV injection.
• Available as tablets, elixir, oral drops, orally disintegrating tablets, sublingual tablets, and injectable preparations.
• Generic hyoscyamine is available.

3. Downsides

If you are between the ages of 18 and 60, take no other medication or have no other medical conditions, side effects you are more likely to experience include:

• Blurred vision, constipation, dizziness, drowsiness, dry mouth, flushing, headache, increased sensitivity to light, and problems with urination are the main side effects reported.
• May impair reaction time and affect a person's ability to drive. Avoid alcohol.
• May cause tachycardia. Ask patients about any preexisting cardiovascular conditions before administration.
• Requires frequent administration 3 to 6 times daily. Some manufacturers recommend administration 30 to 60 minutes before meals.
• May not be suitable for seniors over the age of 65 years.
• May not be suitable for some people including those with heart or lung disease, liver or kidney disease, myasthenia gravis, prostate or thyroid problems, ulcerative colitis, or an intestinal obstruction. Hyoscyamine may also interact with some medications including antidepressants and antipsychotics.
• Be very careful when using in people with known or suspected GI infections because hyoscyamine decreases GI motility and can prevent the expulsion of causative organisms or toxins.
• Long-term use of hyoscyamine may decrease or inhibit salivary flow and contribute to the development of caries, periodontal disease, oral candidiasis, and discomfort.
• The brands NuLev, Symax FasTab, and generic hyoscyamine sulfate (marketed by Ethex) are metabolized to provide 1.7mg, 4.5mg, and 0.5mg of phenylalanine per 0.125mg tablet.
• Do not use hyoscyamine in people with glaucoma.
• Only use during pregnancy if clearly needed. Hyoscyamine crosses the placenta but it is unknown whether it can cause fetal harm or affect reproduction capacity. Animal reproduction studies have shown adverse events on a fetus but there are no controlled studies in humans. Hyoscyamine is excreted into breast milk and use is not recommended.

Note: In general, seniors or children, people with certain medical conditions (such as liver or kidney problems, heart disease, diabetes, seizures) or people who take other medications are more at risk of developing a wider range of side effects. View complete list of side effects

4. Bottom Line

• Hyoscyamine may be used in the treatment of a wide variety of gastrointestinal problems including cramps, bladder control issues, and irritable bowel syndrome. Drowsiness and dry mouth are common side effects.

5. Tips

• May cause drowsiness or blurred vision and affect your ability to drive or operate machinery. Do not drive until you know how hyoscyamine affects you.
• Antacids may interfere with hyoscyamine, reducing its effectiveness. Separate administration (take hyoscyamine an hour before or two hours after antacids).
• Available in many different dosage forms (for example, an oral tablet, disintegrating tablet, sublingual tablet, liquid, and extended-release tablet or liquid). The immediate-release tablets and liquid are usually taken three to four times a day, the extended-release formulations are usually taken twice a day. Take exactly as directed by your doctor and follow the instructions on the label.
• Swallow extended-release tablets whole, do not crush or chew.
• Alcohol may make the side effects of hyoscyamine worse.
• Talk to your doctor about decreasing your dosage if you experience an excessively dry mouth.
• Talk to your doctor urgently if you experience unexplained diarrhea, eye pain, confusion, a fast or irregular heartbeat, or develop a skin rash.
• Be careful in hot or humid climes if taking hyoscyamine as it can decrease your ability to sweat and increase your risk of fever and heat stroke.
• See your doctor urgently if you develop agitation, ataxia (the loss of full control of body movements), confusion, disorientation, eye pain, hallucinations, short-term memory loss, or speech difficulties while taking hyoscyamine.
• Tell your doctor if you are breastfeeding, pregnant, or intending to become pregnant because hyoscyamine may not be suitable for you.

6. Response and effectiveness

• Hyoscyamine works quickly, particularly the sublingual or disintegrating tablets which work within a few minutes. Effects last for six to eight hours (immediate-release formulations) or twelve hours (extended-release formulations).

7. Interactions

Medicines that interact with hyoscyamine may either decrease its effect, affect how long it works, increase side effects, or have less of an effect when taken with hyoscyamine. An interaction between two medications does not always mean that you must stop taking one of the medications; however, sometimes it does. Speak to your doctor about how drug interactions should be managed.

Common medications that may interact with hyoscyamine include:

• antacids, such as aluminum hydroxide or magnesium hydroxide
• antidepressants, such as amitriptyline, clomipramine, desipramine, doxepin, imipramine, nortriptyline, phenelzine, or tranylcypromine
• antihistamines, such as diphenhydramine or promethazine
• antipsychotics, such as chlorpromazine, fluphenazine, haloperidol, perphenazine, risperidone, thioridazine, trazodone, trifluoperazine
• medicines that affect gastrointestinal motility, such as pramlintide
• medicines that affect the heart's rhythm, such as amiodarone, dofetilide, dronedarone, pimozide, quinidine, sotalol, or procainamide.
• others, such as amantadine, belladonna-containing medicines, or potassium supplements.

Avoid drinking alcohol while taking hyoscyamine.

Note that this list is not all-inclusive and includes only common medications that may interact with hyoscyamine. You should refer to the prescribing information for hyoscyamine for a complete list of interactions.

References

• Hyoscyamine elixir. Revised 10/2023. Chartwell RX, LLC. https://www.drugs.com/pro/hyoscyamine-sulfate-elixir.html

Further information

Remember, keep this and all other medicines out of the reach of children, never share your medicines with others, and use hyoscyamine only for the indication prescribed.

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

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