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Thiola EC Side Effects

Generic name: tiopronin

Medically reviewed by Last updated on Jun 7, 2022.

Note: This document contains side effect information about tiopronin. Some of the dosage forms listed on this page may not apply to the brand name Thiola EC.

For the Consumer

Applies to tiopronin: oral tablet, oral tablet delayed release

Side effects requiring immediate medical attention

Along with its needed effects, tiopronin (the active ingredient contained in Thiola EC) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention.

Check with your doctor immediately if any of the following side effects occur while taking tiopronin:

More common

  • Bloating or swelling of the face, arms, hands, lower legs, or feet
  • cloudy urine
  • hives, itching, skin rash
  • pale skin
  • rapid weight gain
  • tingling of the hands or feet
  • trouble breathing
  • unusual bleeding or bruising
  • unusual tiredness or weakness
  • unusual weight gain or loss

Incidence not known

  • Bloody urine
  • blurred vision
  • chest pain or tightness
  • confusion
  • decreased frequency or amount of urine
  • dilated neck veins
  • dizziness
  • dry mouth
  • fainting
  • headache
  • increase in heart rate
  • increased thirst
  • irregular breathing
  • irregular heartbeat
  • lightheadedness
  • loss of appetite
  • lower back or side pain
  • nausea
  • nervousness
  • pounding in the ears
  • rapid breathing
  • slow or fast heartbeat
  • sunken eyes
  • vomiting
  • wrinkled skin
  • yellow skin or eyes

Side effects not requiring immediate medical attention

Some side effects of tiopronin may occur that usually do not need medical attention. These side effects may go away during treatment as your body adjusts to the medicine. Also, your health care professional may be able to tell you about ways to prevent or reduce some of these side effects.

Check with your health care professional if any of the following side effects continue or are bothersome or if you have any questions about them:

More common

  • Bruising
  • cough
  • decreased interest in sexual intercourse
  • diarrhea
  • difficulty in moving
  • fever
  • inability to have or keep an erection
  • large, flat, blue or purplish patches in the skin
  • loss in sexual ability, desire, drive, or performance
  • mouth sores
  • muscle pain or stiffness
  • nausea
  • pain in the joints
  • skin wrinkling
  • stomach pain

Incidence not known

  • Arm, back, neck, or leg pain
  • burning, crawling, itching, numbness, prickling, "pins and needles", or tingling feelings
  • change in or loss of taste
  • chapped lips
  • dry skin
  • excess air or gas in the stomach or bowels
  • feeling of constant movement of self or surroundings
  • full feeling
  • heartburn
  • increased sweating
  • increased weight
  • lack or loss of strength
  • passing gas
  • sensation of spinning
  • stomach discomfort

For Healthcare Professionals

Applies to tiopronin: oral delayed release tablet, oral tablet


Postmarketing reports: Jaundice, liver transaminitis[Ref]


Frequency not reported: Drug fever, rash, fever, arthralgia, lymphadenopathy[Ref]


Very common (10% or more): Nausea (25%), diarrhea/soft stools (18%), emesis (10%), oral ulcers (12%)

Frequency not reported: Abdominal pain, abdominal discomfort, abdominal distension, abdominal pain, chapped lips, dry mouth, dyspepsia, eructation, flatulence, GI disorder, gastroesophageal reflux disease[Ref]


Common (1% to 10%): Anorexia[Ref]


Common (1% to 10%): Rash, ecchymosis, pruritus, urticaria, skin wrinkling

Postmarketing reports: Dry skin, hyperhidrosis, pemphigus foliaceus, skin irritation, skin texture abnormal[Ref]


Common (1% to 10%): Anemia[Ref]


Postmarketing reports: Nephrotic syndrome, renal failure[Ref]


Common (1% to 10%): Cough[Ref]

Nervous system

Postmarketing reports: Vertigo, ageusia, burning sensation, dizziness, dysgeusia, headache, hypoesthesia, asthenia[Ref]


Very common (10% or more): Arthralgia (12%)

Postmarketing reports: Back pain, flank pain, joint swelling, limb discomfort, musculoskeletal discomfort, myalgia, neck pain, pain in extremity[Ref]


Very common (10% or more): Fatigue/malaise (14%), weakness (12%)

Common (1% to 10%): Fever, peripheral edema

Frequency not reported: Hypogeusia (probably due to chelation of trace metals by this drug)

Postmarketing reports: Pain, peripheral swelling, pyrexia[Ref]


Frequency not reported: Proteinuria (including nephrotic syndrome), membranous nephropathy, impotence


Common (1% to 10%): Chest pain

Postmarketing reports: Congestive heart failure, chest pain


1. "Product Information. Thiola (tiopronin)." Mission Pharmacal Company (2001):

Further information

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

Some side effects may not be reported. You may report them to the FDA.