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Hyoscyamine: 7 things you should know

Medically reviewed by Carmen Fookes, BPharm. Last updated on Jun 10, 2020.

1. How it works

  • Hyoscyamine inhibits 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.
  • Twice as potent as atropine, therefore, a lower dosage can be used to provide a similar effect with less potential for adverse reactions.
  • 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 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.
  • Do not use in people with glaucoma.

Notes: 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. For a complete list of all side effects, click here.

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 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.
  • 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, 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.

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 for, 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, macimorelin, 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.


Hyoscyamine. Revised 10/2019.

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.

Copyright 1996-2020 Revision date: June 10, 2020.

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