Asacol Side Effects

Generic Name: mesalamine

Note: This page contains information about the side effects of mesalamine. Some of the dosage forms included on this document may not apply to the brand name Asacol.

Not all side effects for Asacol may be reported. You should always consult a doctor or healthcare professional for medical advice. Side effects can be reported to the FDA here.

For the Consumer

Applies to mesalamine: oral capsule delayed release, oral capsule extended release, oral tablet, oral tablet delayed release, oral tablet enteric coated

In addition to its needed effects, some unwanted effects may be caused by mesalamine (the active ingredient contained in Asacol). In the event that any of these side effects do occur, they may require medical attention.

You should check with your doctor immediately if any of these side effects occur when taking mesalamine:

More common
  • Abdominal or stomach pain (severe)
  • bloody diarrhea
  • rectal bleeding
Less common
  • Abdominal or stomach cramps (severe)
  • blurred vision
  • dizziness
  • fever
  • full or bloated feeling
  • headache (severe)
  • nervousness
  • pounding in the ears
  • pressure in the stomach
  • skin rash and itching
  • slow or fast heartbeat
  • swelling of the abdominal or stomach area
  • unusual tiredness or weakness
  • Anxiety
  • back pain (severe)
  • blue or pale skin
  • chest pain, possibly moving to the left arm, neck, or shoulder
  • chills
  • nausea or vomiting
  • shortness of breath
  • yellow eyes or skin

Some of the side effects that can occur with mesalamine may not need medical attention. As your body adjusts to the medicine during treatment these side effects may go away. Your health care professional may also be able to tell you about ways to reduce or prevent some of these side effects. If any of the following side effects continue, are bothersome or if you have any questions about them, check with your health care professional:

More common
  • Abdominal or stomach cramps or pain (mild)
  • diarrhea (mild)
  • headache (mild)
  • runny or stuffy nose
  • sneezing
Less common
  • Acid or sour stomach
  • acne
  • back or joint pain
  • belching
  • difficulty with moving
  • excess air or gas in the stomach or intestines
  • hair loss or thinning of the hair
  • heartburn
  • indigestion
  • loss of appetite
  • muscle pain or stiffness
  • passing gas
  • stomach discomfort or upset

For Healthcare Professionals

Applies to mesalamine: compounding powder, oral capsule extended release, oral delayed release capsule, oral delayed release tablet, rectal enema, rectal kit, rectal suppository


Colitis symptoms (including cramping, acute abdominal pain, and bloody diarrhea, and occasionally fever, headache, malaise, pruritus, rash, and conjunctivitis) have been exacerbated after starting mesalamine (the active ingredient contained in Asacol) or sulfasalazine in 3% of patients in controlled clinical trials. This acute intolerance syndrome may be difficult to distinguish from a flare of inflammatory bowel disease.

Worsening of colitis or symptoms of inflammatory bowel disease, including melena and hematochezia, have also been reported after commencing mesalamine rectal suspension enema.

Very common (10% or more): Abdominal pain (up to 18%), eructation (up to 16%), nausea (up to 13%)
Common (1% to 10%): Diarrhea (up to 8%), dyspepsia (up to 6%), ulcerative colitis (up to 5.8%), vomiting (up to 5%), constipation (up to 5%), upper abdominal pain (up to 5%), gastrointestinal bleeding (up to 5% or greater), flatulence (up to 5% or greater), acute intolerance syndrome (3%), colitis exacerbation (up to 3%), lower abdominal pain (less than 3%), rectal hemorrhage (less than 3%), gastroenteritis (2% or greater), gastrointestinal hemorrhage (2% or greater), stool abnormalities (color or texture change; up to 2% or greater), tenesmus (up to 2% or greater), rectal disorder (2% or greater), abdominal enlargement (up to 2% or greater), abdominal distention (up to 1.3%)
Rare (less than 0.1%): Colitis, pancreatitis, rectal polyp, duodenal ulcer, esophageal ulcer, dysphagia, fecal incontinence, oral moniliasis, thirst, recurrence of ulcerative colitis, gastritis, stomatitis, perforated peptic ulcer
Frequency not reported: Worsening of colitis or symptoms of inflammatory bowel disease (including melena and hematochezia), elevated amylase, elevated lipase
Postmarketing reports: Pancreatitis, gastritis, dry mouth, oral ulcers, gastroenteritis, gastrointestinal bleeding, perforated peptic ulcer, bloody diarrhea, taste perversion

Nervous system

Very common (10% or more): Headache (up to 35%)
Common (1% to 10%): Dizziness (up to 8%), lightheadedness (8%), faintness (8%), tinnitus (less than 3%), vertigo (less than 3%), migraine (2% or greater), paresthesia (up to 2% or greater), insomnia (up to 2%)
Rare (less than 0.1%): Benign intracranial hypertension (at least 1 case)
Postmarketing reports: Systemic lupus erythematosus, peripheral neuropathy, Guillain-Barre syndrome, transverse myelitis, somnolence, tremor, hyperesthesia, tinnitus, vertigo

A 23-year-old female with ulcerative colitis who had been taking 400 mg mesalamine tablets three times a day developed benign intracranial hypertension. The examination disclosed benign intracranial hypertension that resolved when mesalamine was discontinued and recurred when the drug was restarted.


Very common (10% or more): Muscle aches (21%)
Common (1% to 10%): Back pain (up to 7%), arthralgia (up to 5% or greater), hypertonia (5%), myalgia (up to 3%), joint disorder (2% or greater), arthritis (2%)
Frequency not reported: Leg cramps, rheumatoid arthritis
Postmarketing reports: Gout, myalgia


A 72-year-old female with ulcerative colitis who had begun taking two 400 mg mesalamine (the active ingredient contained in Asacol) tablets twice daily experienced pleural effusion and pulmonary infiltrates. Chest radiograph showed bilateral pleural effusions and an infiltrate in the lower lobe of the right lung. It was determined that the adverse events described appeared likely to be due to mesalamine therapy.

Pleural effusion and pulmonary infiltrates, generally accompanied by eosinophilia, have been reported rarely. More severe cases have included fibrosing alveolitis.

Very common (10% or more): Nasopharyngitis (up to 11%)
Common (1% to 10%): Rhinitis (up to 9%), influenza and influenza-like illness (up to 5% or greater), sinusitis (3%), dyspnea (less than 3%), bronchitis (2% or greater), increased cough (2%)
Rare (less than 0.1%): Pleural effusion, pulmonary infiltrates, fibrosing alveolitis
Postmarketing reports: Eosinophilic pneumonia, interstitial pneumonitis, asthma exacerbation, pleuritis, pneumonitis, hypersensitivity pneumonitis, allergic alveolitis


Common (1% to 10%): Chest pain of unknown etiology (3%), vasodilation (up to 2% or greater)
Uncommon (0.1% to 1%): Hypertension (up to 1%)
Rare (less than 0.1%): Tachycardia, hypotension, palpitations, pericarditis, pericardial effusion, myocarditis, T-wave abnormalities, severe symptomatic sinus bradycardia (at least 1 case), pleuropericarditis (at least 1 case)
Postmarketing reports: Angioedema, myocarditis, pericardial effusion, pericarditis

One 20-year-old patient died of cardiac arrhythmias attributed to myocarditis 13 days after starting mesalamine.

A 56-year-old male with hypertension and ulcerative proctitis experienced pleuropericarditis coincident with mesalamine therapy. Evaluation revealed acute pleuropericarditis manifested by ECG changes, pericardial effusion, and a small pleural effusion. All symptoms resolved when mesalamine was discontinued.


Very common (10% or more): Pain (in various parts of the body; up to 14%)
Common (1% to 10%): Asthenia (up to 7%), fever (up to 6%), chills (3%), peripheral edema (3%), fatigue (up to 3%), ear disorder (2% or greater), infection (2% or greater), malaise (2%)
Frequency not reported: Pyrexia, pharyngolaryngeal pain, ear pain, ear congestion
Postmarketing reports: Lupus-like syndrome, drug fever, neck pain, facial edema, edema


Common (1% to 10%): Rash (up to 7%), sweating (up to 3%), pruritus (up to 3%), alopecia (less than 3%), acne (up to 2%)
Rare (less than 0.1%): Lupus erythematosus-like reactions, prurigo, eczema, lichen planus, nail disorder, photosensitivity, folliculitis
Postmarketing reports: Psoriasis, alopecia, pyoderma gangrenosum, dry skin, erythema nodosum, urticaria, Stevens-Johnson syndrome


Common (1% to 10%): Decreased hematocrit and hemoglobin (less than 3%)
Rare (less than 0.1%): Agranulocytosis, aplastic anemia
Frequency not reported: Neutropenia, pancytopenia, ecchymosis, thrombocythemia, decreased platelet count
Postmarketing reports: Granulocytopenia, agranulocytosis, aplastic anemia, thrombocytopenia, eosinophilia, leukopenia, anemia, lymphadenopathy


Common (1% to 10%): Rash and pruritus (greater than 2%); arthralgias, myalgias, and fever (greater than 1%)
Uncommon (0.1% to 1%): Allergic reactions (which could involve eosinophilia), hepatitis, interstitial pneumonitis, pericarditis
Rare (less than 0.1%): Hypersensitivity reactions (such as hypersensitivity pneumonitis, angioedema, erythroderma, toxic epidermal necrolysis, palmar-plantar erythrodysesthesia, hypereosinophilia), pruriginous rash (at least 2 cases)
Frequency not reported: Mesalamine-induced cardiac hypersensitivity reactions (myocarditis and pericarditis)
Postmarketing reports: Anaphylactic reaction, drug reaction with eosinophilia and systemic symptoms (DRESS)

A male patient with ulcerative colitis experienced pruriginous rash coincident with mesalamine therapy. He experienced the cutaneous hypersensitivity reaction 48 hours after initiating therapy with mesalamine 500 mg orally every 8 hours. After mesalamine was suspended and antihistamines were given, the patient recovered. Upon reintroduction of mesalamine, the symptoms appeared again 24 hours later.


Common (1% to 10%): Cholestatic hepatitis (less than 3%), elevated transaminases (less than 3%), abnormal liver function test (up to 2.3%)
Rare (less than 0.1%): Granulomatous hepatitis (at least 1 case)
Frequency not reported: Hepatitis (presenting with rash, fever, abdominal pain, nausea, vomiting, chills, dizziness, hepatomegaly, lymphadenopathy, and laboratory abnormalities [including elevated liver function tests, eosinophilia, and leukocytosis]), hepatic impairment, jaundice, cholestatic jaundice, cirrhosis, liver necrosis, liver failure, Kawasaki-like syndrome (including changes in liver enzymes), transient elevations in liver function tests, hypersensitivity hepatitis, hepatic failure
Postmarketing reports: Elevated AST (SGOT) or ALT (SGPT), elevated gamma-glutamyltransferase, elevated bilirubin, hepatitis, jaundice, cholecystitis, cholestatic jaundice, liver necrosis, liver failure, Kawasaki-like syndrome (including changes in liver enzymes)

A 42-year-old male with ulcerative colitis was admitted for investigation of prolonged fever associated with cholestatic liver tests. Endoscopic retrograde cholangiopancreatography demonstrated a normal biliary tree, and liver biopsy showed granulomata. The symptoms disappeared after cessation of mesalamine therapy and recurred on rechallenge.

Hypersensitivity hepatitis associated with mesalamine appears to occur less commonly than with sulfasalazine.

Hepatic failure has been reported in patients with preexisting liver disease.


Renal impairment (including minimal change nephropathy, acute and chronic interstitial nephritis, and, rarely, renal failure) has been reported with products that contain mesalamine (the active ingredient contained in Asacol) or are converted to mesalamine.

Renal tubular dysfunction has been reported, although a definitive causality has not been established.

Common (1% to 10%): Decreased creatinine clearance (less than 3%)
Frequency not reported: Nephrogenic diabetes insipidus, nephrotic syndrome, renal impairment, renal tubular dysfunction
Postmarketing reports: Renal failure, interstitial nephritis, minimal change nephropathy, elevated blood urea nitrogen, elevated serum creatinine


Common (1% to 10%): Dysmenorrhea (3%), hematuria (less than 3%), urinary frequency (2% or greater)
Rare (less than 0.1%): Oligospermia, infertility in men
Frequency not reported: Albuminuria, amenorrhea, breast pain, hypomenorrhea, metrorrhagia, urinary burning
Postmarketing reports: Dysuria, urinary urgency, hematuria, epididymitis, menorrhagia, reversible oligospermia

Rarely, oligospermia and infertility in men have been reported and have been attributed to sulfasalazine.


Common (1% to 10%): Anxiety (2% or greater), nervousness (2% or greater)
Frequency not reported: Lethargy, mild disorientation, decreased libido
Postmarketing reports: Depression, emotional lability, confusion


Common (1% to 10%): Elevated triglycerides (less than 3%)
Postmarketing reports: Anorexia, increased appetite, elevated alkaline phosphatase, elevated lactate dehydrogenase


Common (1% to 10%): Vision abnormalities (2% or greater), conjunctivitis (up to 2%)
Postmarketing reports: Eye pain, blurred vision


Rectal suspension enemas:
Common (1% to 10%): Pain on insertion of enema tip (1.35%), hemorrhoids (1.35%), rectal pain (1.23%)
Uncommon (0.1% to 1%): Rectal pain/soreness/burning (0.61%)
Frequency not reported: Perianal irritation

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