Hyoscyamine is an anticholinergic and antispasmodic medication used to relieve muscle spasms in the digestive, urinary, and biliary tracts. It works by blocking acetylcholine, a chemical messenger that triggers involuntary muscle contractions and gland secretions.
This medication comes from plants in the Solanaceae family, such as Atropa belladonna and Datura stramonium. It belongs to a group of natural compounds called tropane alkaloids and is closely related to atropine and scopolamine, which have similar effects on the body.
In the United States, hyoscyamine is available by prescription in several forms, including tablets, oral solutions, and sublingual tablets. Although widely used for many years to treat digestive and urinary problems, it is considered a “grandfathered” medication, meaning it has been on the market since before modern FDA approval standards were introduced.
Indications for use
Hyoscyamine is mainly prescribed to relieve muscle spasms and cramping in the gastrointestinal tract. It is often used to manage symptoms of irritable bowel syndrome (IBS), diverticulitis, and peptic ulcers. It can also help reduce bladder spasms caused by conditions like interstitial cystitis, neurogenic bladder, or the placement of ureteral stents.
Doctors may also prescribe hyoscyamine to relieve pain from biliary or kidney colic, decrease excessive saliva production in people with Parkinson’s disease (sialorrhea), or help control intestinal movement during certain medical procedures.
In some cases, hyoscyamine is used off-label to help manage irregular heart rhythms caused by cholinesterase inhibitors or to reduce secretions before surgery.
How to take it
Hyoscyamine is available in several forms, including regular tablets, orally disintegrating tablets, sublingual tablets, oral solutions, drops, and extended-release tablets. The prescribed form depends on the condition being treated and how long the medication needs to work.
For adults, the usual oral dose is 0.125 to 0.25 mg every 4 hours as needed, with a maximum daily dose of 1.5 mg. The extended-release version is typically taken at 0.375 to 0.75 mg every 12 hours. Sublingual tablets dissolve under the tongue and work quickly, while extended-release tablets provide longer-lasting effects.
Hyoscyamine can be taken with or without food. Extended-release tablets should be swallowed whole and not crushed or chewed. People with liver or kidney problems may need dosage adjustments to avoid side effects.
Possible side effects
Common side effects of hyoscyamine include dry mouth, blurred vision, constipation, drowsiness, difficulty urinating, and a faster heart rate. Some people may also experience dizziness, headache, or sensitivity to heat due to reduced sweating.
Serious side effects are rare but can include confusion, hallucinations, or a rapid heartbeat. These are more likely to occur in older adults or people taking other medications with anticholinergic effects.
In cases of overdose, symptoms of anticholinergic toxicity may develop, such as agitation, flushed skin, dilated pupils, or trouble breathing. Anyone experiencing these symptoms should seek emergency medical attention immediately.
Contraindications for use
Hyoscyamine should not be used by people with glaucoma, myasthenia gravis, bowel or urinary blockages, or severe ulcerative colitis. It should also be avoided in those with unstable heart conditions, such as arrhythmias or heart failure.
Older adults should use hyoscyamine with extra caution because they are more sensitive to anticholinergic effects and may be at higher risk for confusion, dizziness, or falls.
During pregnancy, hyoscyamine should only be taken if clearly needed, as there is limited information about its safety for the baby. It passes into breast milk, so use during breastfeeding should only occur under medical supervision.
Drug interactions
Hyoscyamine can interact with other medications that have anticholinergic properties, including certain antihistamines, tricyclic antidepressants, and some antipsychotic drugs. Taking these together can increase the risk of side effects.
Antacids may reduce the absorption of hyoscyamine if taken at the same time, and the medication can enhance the sedative effects of narcotic pain relievers or sleep medications.
People taking drugs for heart disease, glaucoma, or urinary retention should talk to their healthcare provider before using hyoscyamine.
Precautions and special populations
Older adults and people with liver or kidney impairment should use hyoscyamine carefully, as it may build up in the body and increase the risk of side effects. Those who spend time outdoors or in hot environments should take extra precautions, since hyoscyamine reduces sweating and may increase the risk of overheating or heat stroke.
If taken regularly, hyoscyamine should not be stopped suddenly without medical advice. Dosages may need to be adjusted gradually based on individual response and tolerance.