RIMSO-50 Side Effects: What to Expect and When to Call Your Doctor

If you are about to start RIMSO-50 (dimethyl sulfoxide) bladder instillation therapy for interstitial cystitis, you may have heard about some of the drug's unusual side effects — particularly the strong garlic odor. Knowing what to expect ahead of time can help you prepare and avoid unnecessary alarm.

This guide covers the common and serious side effects of RIMSO-50, explains why they happen, and tells you when to contact your healthcare provider.

Common Side Effects of RIMSO-50

1. Garlic-Like Taste and Odor — The Most Well-Known Effect

Within minutes of receiving a RIMSO-50 instillation, most patients notice a strong garlic-like or onion-like taste in their mouth. This is completely normal and happens because dimethyl sulfoxide is rapidly absorbed through the bladder wall into the bloodstream, where it is metabolized to dimethyl sulfide — a compound responsible for the distinctive odor.

Taste: Typically begins within minutes of instillation and may last several hours.

Odor on breath and skin: Can persist for up to 72 hours (3 days) after treatment. This is due to dimethyl sulfide being eliminated through the lungs and skin.

What to do: Nothing needs to be done — this is expected. You may want to plan treatments before days off from work or social events. The odor is not a sign of a problem.

2. Bladder Discomfort or Pain During Instillation

Many patients experience mild to moderate bladder discomfort when RIMSO-50 is instilled. This discomfort typically decreases with each successive treatment as the bladder adjusts. For patients with very sensitive bladders, the first one to three sessions may be performed under anesthesia (often a saddle block) to minimize discomfort.

Your provider may administer oral analgesics or belladonna-and-opium suppositories before the instillation to reduce bladder spasm. Lidocaine jelly is typically applied to the urethra before catheter insertion to minimize discomfort during the procedure.

3. Transient Chemical Cystitis

Some patients develop a temporary increase in bladder irritation and urgency following RIMSO-50 treatment — called transient chemical cystitis. This typically resolves on its own within 1–2 days. It is not a sign that the treatment isn't working; in fact, some providers view it as evidence that DMSO is penetrating the bladder lining.

Serious Side Effects to Watch For

4. Allergic or Anaphylactoid Reaction (Rare)

Dimethyl sulfoxide can cause the release of histamine, and in rare cases, a hypersensitivity reaction has been reported. Signs of a serious allergic reaction include:

Difficulty breathing or shortness of breath

Swelling of the face, lips, tongue, or throat

Hives or widespread rash

Rapid heartbeat or feeling faint

Action: RIMSO-50 is administered in a clinical setting precisely so that trained staff can respond to reactions like this. Tell your provider immediately if you experience these symptoms during or after an instillation.

5. Potential Eye Effects With Long-Term Use

Studies in animals (monkeys, dogs, rabbits) given high doses of dimethyl sulfoxide showed changes in the refractive index of the lens and lens opacities. While this has not been definitively demonstrated in humans at therapeutic intravesical doses, providers typically recommend periodic eye exams for patients on long-term RIMSO-50 therapy as a precautionary measure. Report any vision changes to your doctor promptly.

Lab Monitoring During RIMSO-50 Treatment

Your provider may order periodic blood tests (complete blood count, liver function tests) and urine tests during RIMSO-50 treatment to monitor for any effects on your kidneys, liver, and blood cells. These are routine precautions. Keep all scheduled lab and eye exam appointments.

Side Effects That Improve With Time

A key point that reassures many patients: the discomfort associated with RIMSO-50 instillation typically decreases with repeated treatments. Research and clinical experience consistently show that pain and urgency during and after instillation lessens as the course of treatment progresses. By the third or fourth session, many patients tolerate the procedure much more comfortably.

When to Call Your Doctor After a RIMSO-50 Treatment

Severe or worsening bladder pain that doesn't improve within 2 days

Signs of urinary tract infection (fever, chills, burning with urination, cloudy urine)

Any vision changes or eye discomfort

Allergic reaction symptoms (hives, difficulty breathing, swelling)

Blood in urine (hematuria) beyond a trace amount

For information about drug interactions with RIMSO-50, see: RIMSO-50 Drug Interactions: What to Avoid and What to Tell Your Doctor.

If you are having difficulty finding RIMSO-50 in stock near you, medfinder can help by searching pharmacies in your area to locate which ones have it available.