Medication
Medication and its side effects
The medicines that treat IgG4-related disease work well, and like all effective medicines they can bring side effects. Knowing what is common, why it happens, and when it matters can make the whole thing less frightening. Many side effects are mild or ease as doses come down, while some need prompt attention, so it helps to tell your team about anything new or worsening.
This page explains what is known. It cannot tell you what is happening in your own body. If something worries you, or matches the 'when to seek care' signs below, contact your doctor. In an emergency, seek urgent care first. Information can wait. Safety cannot.
Part A — The medicines and what they can cause
A short card for each medicine used in IgG4-related disease. Most side effects settle with time or as the dose comes down.
Steroids (e.g. prednisone)
An anti-inflammatory medicine, usually given as tablets.
Why: Calm inflammation fast; usually the first treatment.
Common side effects: Trouble sleeping, raised blood sugar, reflux or heartburn, mood changes, increased appetite.
Most are dose-related and ease as the dose is lowered. Steroids are reduced step by step under your specialist's guidance and are not stopped suddenly. With longer use, your team monitors things like bone health, blood pressure, blood sugar, eyes, and mood.
Steroid-sparing medicines (e.g. azathioprine, mycophenolate, methotrexate)
An immune-calming tablet taken alongside or after steroids.
Why: Added so steroids can be reduced.
Common side effects: Stomach upset, nausea, bloating, especially in the first weeks; higher infection risk.
Stomach effects often settle as the body adjusts.
Rituximab
An antibody treatment given by drip (infusion).
Why: Targets specific immune cells (B cells) involved in IgG4-RD.
Common side effects: Infusion-related reactions during or after the drip; higher infection risk.
Given and monitored in a hospital setting.
Inebilizumab (brand name Uplizna), approved 2025
The first medicine authorised specifically for active IgG4-related disease in adults.
Why: An anti-CD19 antibody that reduces the B cells involved in IgG4-RD.
Common side effects: Infusion-related reactions; higher infection risk; low blood cell counts.
Given and monitored by a specialist, with screening and checks before and during treatment.
Obexelimab, published and not approved
An antibody given as a weekly injection under the skin. It is not an approved treatment for IgG4-related disease.
Why: It binds to CD19 on the B cell together with an inhibitory receptor, which quietens the cell rather than destroying it.
What the trial found: In the phase 3 INDIGO trial, funded by the manufacturer and published in June 2026, 194 people received either obexelimab or a dummy injection for a year, with everyone coming off steroids by week eight. Flares happened in about 27 of every 100 people on obexelimab and about 55 of every 100 on placebo. About 37 in 100 reached full remission at one year against about 20 in 100 on placebo, and people on obexelimab needed roughly a third as much rescue steroid.
Common side effects: Joint pain, allergic-type reactions and diarrhoea were reported more often than on placebo. Serious side effects were less common on obexelimab than on placebo.
Not approved, and not available as a treatment. Ask your own specialist whether a trial is open to you.
Rilzabrutinib, the one that is a tablet
An experimental medicine taken by mouth. It is not an approved treatment for IgG4-related disease.
Why: It blocks an enzyme called BTK that carries signals inside B cells. Being a tablet sets it apart from rituximab, inebilizumab and obexelimab, which are given by drip or by injection.
What the trial found: In an early phase 2 study run by the manufacturer, 27 people took it for up to a year, some who had not improved on rituximab and some who had not tried it. Nineteen of the 27 were free of flares and off steroids and other immune-suppressing medicines by the end.
Common side effects: Diarrhoea was the most common. Serious side effects occurred in two of the 27, including one death that the trial investigators judged unrelated to the medicine.
Everyone in that study received the drug. With no comparison group and only 27 people, the findings point the way rather than settle it. A larger trial comparing rilzabrutinib against a dummy treatment is now recruiting.
Medicines that manage the side effects
Extra medicines added to protect against known effects of the main treatment.
Why: Doctors often prescribe a second medicine to control a side effect.
Common side effects: For example a stomach-protecting medicine (a proton-pump inhibitor such as lansoprazole) for reflux, or medicines to manage blood sugar while on steroids.
These are a normal part of treatment, not a sign something is wrong.
Part B — Common side effects, with a reassure / discuss / act now guide
For each side effect: what it is and why the medicine can cause it, then three levels — what is usually expected, what is worth raising at your next appointment, and what should prompt urgent contact.
1. Reflux and heartburn
Why: Steroids increase stomach acid; some medicines slow the stomach, so acid pushes back up. A stomach-protecting medicine is often prescribed alongside, and it does its job well.
Usually normalMild heartburn that eases with the protecting medicine, smaller meals, and not lying down soon after eating.
Raise at your next appointmentReflux that keeps disturbing sleep or isn't controlled by the current medicine.
Seek care promptlyBlack or tarry stools, vomiting blood, severe or new upper-abdominal pain, difficulty swallowing.
2. Trouble sleeping (insomnia)
Why: Steroids keep the body's stress system active; the effect is strongest at higher doses and usually eases as the dose comes down.
Usually normalLighter or broken sleep at higher steroid doses.
Raise at your next appointmentSleep that stays poor as the dose lowers, or is wearing you down.
Seek care promptlyThoughts of harming yourself, or a sudden severe change in mood or thinking.
3. Raised blood sugar
Why: Steroids raise blood sugar; some people need medicine to manage it while on treatment. It often improves as steroids reduce.
Usually normalHigher readings while on higher steroid doses, especially after meals, when your team is aware and monitoring.
Raise at your next appointmentReadings creeping up, or a pattern you want reviewed.
Seek care promptlyVery high readings with intense thirst, frequent urination, confusion, drowsiness, or a fruity smell on the breath.
4. Mood changes and restlessness
Why: Steroids affect mood and tension; these are dose-related and tend to ease as the dose drops.
Usually normalFeeling wired or restless at higher doses.
Raise at your next appointmentMood changes that trouble you or those around you.
Seek care promptlyThoughts of harming yourself, severe agitation, or losing touch with what's real.
5. Higher risk of infection
Why: Medicines that calm the immune system also lower its guard. This is expected and managed with monitoring.
Usually normalBeing told to watch for infections and take sensible precautions.
Raise at your next appointmentMinor infections that are slow to clear.
Seek care promptlyFever, shaking chills, a cough with breathlessness, or feeling suddenly very unwell.
Steroids can raise your blood sugar and shift your blood pressure. Our free log app lets you track your readings and hand your doctor a clean report at your next appointment.
Open the readings logIf you take steroids, it can help to carry a card that tells anyone treating you in an emergency that your steroids must not be stopped suddenly.
Patient alert cardThis is general information about known side effects, not advice about your own situation. Your specialist knows your case. Bring anything here that concerns you to them.
Sources
Based on the prescribing information for these medicines, the international consensus guidance on IgG4-related disease management (Khosroshahi A, et al., 2015), and these trial publications: Della-Torre E, Baker MC, Zhang W, et al; INDIGO Trial Investigators. Obexelimab for the Treatment of IgG4-Related Disease. N Engl J Med, published online 2 June 2026. doi 10.1056/NEJMoa2601337; Stone JH, Carruthers M, Baker MC, et al. A phase 2 trial of rilzabrutinib in IgG4-related disease. Ann Rheum Dis 2026. doi 10.1016/j.ard.2026.05.017. Always confirm with your own doctor.
This assistant shares sourced information and cannot diagnose you or replace your doctor. In an emergency, seek urgent care first.
