Bentyl side effects and drug information

Bentyl (dicyclomine hydrochloride) is an anticholinergic and antispasmodic drug that comes in 3 forms with varying dosages which are:

  • Bentyl capsule 
  • Bentyl tablet 
  • Bentyl injection
PubChem CID 3042
Trade name Byclomine, Bentyl, Dibent
ChEMBL Id 1123
ChemSpider ID 2934
Molar mass 309.487 g/mol


Bentyl (dicyclomine hydrochloride) is an anticholinergic and antispasmodic drug that comes in 3 forms with varying dosages which are:

  • Bentyl capsule which is made up of 10mg dicyclomine hydrochloride and is intended for oral use.
  • Bentyl tablet has 20mg of dicyclomine hydrochloride and is for oral use as well.
  • Bentyl injection is supplied as an ampoule that consists of 20mg/2ml or 10mg/ml, where each ml is composed of 10mg dicyclomine hydrochloride USP in sterile water. This form is a sterile, aqueous solution and pyrogen-free that is only intended for intramuscular injection and not for intravenous usage.

Dicyclomine hydrochloride appears as a fine crystalline that is an odorless powder and is white but has a bitter taste. It easily dissolves in water, alcohol, and chloroform, but only slightly in ether.

Side Effects

The use of this medication may include some side effects which are usually associated with dosage consumption and are generally reversible when the treatment is done or stopped.  

Clinical Trials Experience

In some clinical trials with more than 100 patients that were given dicyclomine hydrochloride to treat irritable bowel syndrome, the starting dosage was 160mg per day or 40mg 4x daily.

61% of the patients experienced anticholinergic side effects. Among the population that was part of the study, 9% discontinued Bentyl as they had one or more symptoms of side effects; while 41% who also had side effects, continued with the treatment of 160mg per day dosage and the side effects were either tolerated or eventually went away. 46% of the patients with side effects had dose reduction from 160mg to 90mg, and the side effects were also tolerated or disappeared.

Post Marketing Experience

During the post-approval of Bentyl, some adverse side effects were determined along with their potential symptoms.

  • Disorder in the skin and subcutaneous tissue: rash, dermatitis allergic, erythema
  • Disorder in the eye: mydriasis, blurred vision, cycloplegia
  • Psychiatric disorder: delirium, agitation, hallucination, delusion, confusion, mania, mood changes, pseudodementia, amnesia
  • Cardiac disorder: tachyarrhythmias, palpitations
  • Disorder in the immune system: drug hypersensitivity
  • Disorder in the respiratory, mediastinal, thoracic: nasal congestion, dyspnea
  • Disorder in the nervous system: syncope, somnolence, dizziness, headache
  • Disorder in the breast and reproductive system: suppressed lactation
  • Disorder in the gastrointestinal tract: vomiting, nausea, constipation, dry mouth, dyspepsia, abdominal pain and distension
  • General disorder: malaise, fatigue

Reactions after IV injection of Bentyl:

  • Thrombosis
  • Local pain, change in skin color, reflex sympathetic dystrophy syndrome in the site of injection
  • Thrombophlebitis

Adverse reactions with drugs of similar nature:

  • Central nervous system: insomnia, numbness, tingling, dyskinesia, speech disturbance
  • Respiratory system: apnea
  • Gastrointestinal: anorexia
  • Cardiovascular system: hypertension
  • Peripheral nervous system: neuromuscular blockage
  • Ophthalmologic: increased ocular tension, diplopia
  • Allergic reaction: itching, urticarial

Other possible side effects:

  • Sneezing
  • Impotence
  • Throat congestion
  • Decreased sweating

Reactions after intramuscular injection of Bentyl:

  • Local irritation
  • Focal coagulation necrosis

Reactions after using the injectable form:

  • Temporary lightheadedness

Indication and Dosage

For adults

The starting dose is 20mg 4x daily. Dosage may be increased to 40mg 4x times daily after one week of treatment. If, after two weeks, there is no sign of improvement, and the dosage falls below 80mg, treatment should be stopped.

Intramuscular Administration in Adults

Intramuscular injection should only be administered through this procedure, and the recommended dosage is 10 to 20mg 4x daily. This form of administration may only be used for 1 to 2 days, and only if the patient cannot tolerate oral administration.

Drug Interaction

This medication interacts with the following drugs:

  • Other medicines that have anticholinergic reactions
  • Those with antiglaucoma properties
  • Other medicines for gastrointestinal motility
  • Antacids

Warnings and Precautions

The use of the Bentyl solution that is intended for intramuscular administration should solely be used for that purpose. Misuse of this product may lead to thrombosis, thrombophlebitis, and reactions in the injection site.

Dicyclomine hydrochloride should be used with caution for those with these conditions:

  • Cardiovascular system issues
  • Disorder in the central and peripheral nervous system
  • Myasthenia gravis
  • Hepatic and renal illness
  • Ulcerative colitis
  • Prostatic hypertrophy
  • Gastrointestinal issues
  • Elderly as they are more prone to experience side effects
  • Other nonclinical toxicology

Overdose and Contraindications

Should there be a case of overdose, the patient should seek medical attention or contact the poison control center.

Overdose has these symptoms: blurred vision, headache, vomiting, nausea, dilated pupils, hot and dry skin, dry mouth, dizziness, trouble swallowing, convulsion, curare- like reaction, abdominal and flank pain, numbness on the left side, cold fingertips, nervousness, and decreased appetite.

These experiences though, disappeared when treatment was discontinued, and the likelihood that the symptoms would be life-threatening has not been confirmed.  

Bentyl should not be administered to infants who are younger than six months old, breastfeeding mothers, and people who have conditions such as:

  • Glaucoma
  • Reflux esophagitis
  • Myasthenia gravis
  • Severe ulcerative colitis
  • Unstable cardiovascular issues
  • Obstructive uropathy
  • Obstruction in the gastrointestinal tract

Clinical Pharmacology

Mechanism of Action

Dicyclomine works to provide relief for smooth muscle spasm of the gastrointestinal tract. Based on animal trials, this reaction is achieved through two mechanisms. One is a specific anticholinergic reaction at the acetylcholine- receptor site with about 1/8mg of atropine potency. Another one is a direct effect on the smooth muscle.


This product may hinder sweating, production of saliva, lessen secretions in the gastrointestinal tract, and motility. It may also cause drowsiness, increase in heart rate, pupil dilation, and inhibit motor function.


Absorption and Distribution

Dicyclomine is quickly absorbed in the body with peak values around 1 hour to 1.5 hours, and the mean volume of distribution for an oral dose of 20mg is about 3.65L/kg.


The main route of elimination is through urine. The fecal route is also possible, but to a lesser degree.

Clinical Studies

Based on controlled clinical studies with more than 100 patients suffering from irritable bowel syndrome who were treated with this drug, 82% of those who had 160mg starting dose showed favorable clinical reactions as opposed to the 55% who had placebo treatment.

Medication Guide

Bentyl should not be used to treat infants younger than six months old and breastfeeding mothers.

This medication may cause drowsiness, do not drive, or use machinery when using this product, and it may cause reactions in high-temperature situations that may result from heating stroke and fever because of a decrease in sweating