Most stem cell treatments have no acute complications. Most is not all.
This page exists because patients deserve a candid conversation about what can go wrong, what we've actually seen, and how the program is structured to handle it. Most clinic websites avoid this topic. The avoidance is itself a signal: a program that has thought carefully about safety doesn't need to bury the question, it needs to answer it.
The honest framing: across thousands of treatments the most common adverse event is mild flu-like symptoms the evening of treatment, in a subset of patients. The rest is rare. None of it is something the program is unprepared for.
Prefer to watch?
What we tell you, before you ask.
This page is a 9-minute read. The video walks through the honest answer: what happens if something goes wrong, and how a complication is handled. Keep scrolling for the full version.
What patients actually encounter, by frequency.
Adverse events in MSC therapy occupy a clear spectrum: predictable mild reactions in a small minority, expected procedural soreness for direct-injection patients, and rare serious events that are well-characterised in the published literature. The chart below puts the rates side by side.
By frequency, not by feeling.
The most common predictable reaction.
A subset of IV patients experience a mild flu-like syndrome the evening of treatment. The symptoms are typical: low-grade fever, mild body aches, some fatigue, occasionally a slight headache. They begin a few hours after the infusion and typically resolve overnight. A minority of patients carry the symptoms into the next morning before they fully clear.
These symptoms are mild and self-limited. Patients are monitored throughout the infusion, simple over-the-counter support is available if a patient wants it, and the clinical team checks in that evening or the next morning to confirm the patient is back to baseline. The check-in is documented in the chart.
The expected response to a joint or spinal injection.
Patients receiving direct injections: into a knee, hip, shoulder, hand, foot joint, or a spinal/disc compartment, can expect a different category of post-treatment experience. The soreness that follows is not an adverse event. It's the intended biological response: the inflammatory cascade that triggers cytokine release, paracrine signalling, and recruitment of local repair cells.
Drag the timeline. See where the body is.
The acute window is the therapeutic mechanism, patients are advised to avoid NSAIDs through it. Function frequently exceeds pre-treatment baseline from week 6 onward.
Patients with soreness substantially outside this window: more severe than expected, lasting longer than two weeks, or accompanied by signs of infection, are flagged for medical review. The team distinguishes between expected post-procedural inflammation and signs of an actual complication.
What can actually go wrong in MSC therapy.
Across the published clinical literature and the operational experience of established programs, the categories of rare adverse events are well-characterised. Each has a known response.
Anaphylactic-type reactions
Patients can react to the cells or residual manufacturing components. Reactions during IV infusion are very rare in cord-derived MSC literature, but not zero.
Vasovagal during injection
Brief lightheadedness, nausea, or drop in blood pressure during or immediately after a direct injection. Most resolve within minutes with positioning.
Injection-site infection
Any procedure that breaks skin carries some infection risk. Mitigated by sterile technique in the suite and cGMP standards in the cell preparation.
Underlying medical event
A cardiac event, stroke, or other acute medical issue while in the treatment chair may or may not be related to the therapy. The response matters more than the cause.
Non-viable cell response
If a clinic delivers cells that are largely non-viable, dead cells trigger a pro-inflammatory response rather than the anti-inflammatory effect intended.
Late symptoms after return
Symptoms emerging days or weeks after treatment require local evaluation. Continuity of records across borders is part of the protocol.
How serious adverse events are managed.
A Serious Adverse Event (SAE) is any medical event during or after treatment that results in hospitalisation, prolongs an existing stay, causes lasting harm, or threatens life. Programs that say "we've never had a problem" without being able to describe what would happen if they did are not the same as programs with a real SAE infrastructure.
What happens, in order.
Each phase is owned, documented, and handed off cleanly to the next. Press play to walk through, or click any phase.
treatment
Real-time response, in the building.
Any acute event during the treatment session is managed in real time by the attending physician and the hospital's medical resources. The patient is moved to the appropriate level of care within the hospital if needed, with continuity of clinical team and continuity of records.
discharge
Observation, then release.
Patients are observed for a defined period after treatment before discharge. Vitals, symptom report, and a physician check confirm the patient is stable for return travel. Any concern delays discharge and may convert the visit into an overnight observation stay.
travel
Evening check, at the hotel.
Patients remain in San Diego (local hotel) for the evening, with the clinical team available by phone. The patient-care coordinator follows up that evening or the next morning. For patients with mild flu-like symptoms, this is where they're confirmed and reassurance is provided.
return
Local care, connected.
If a serious event occurs after return, the patient is directed to local emergency care, with Celva providing whatever documentation US providers need to assess the case: the certificate of analysis, the clinical record from the visit, the contact information for the treating physicians for direct consultation.
& learn
Reviewed, incorporated.
Every SAE is documented, reviewed by the clinical team, and incorporated into protocol refinement where applicable. Across the program's operational history, the cumulative incidence of SAEs related to the treatment itself has been very low. The structured documentation is what allows the program to make that statement with confidence rather than as a guess.
"Walk me through what happens if I have a reaction during the infusion, minute by minute, room by room." The acceptable answer names the team, the unit, and the timing. An evasive answer or one that ends with "we call 911" is your answer.
The honest framing for your decision.
The risk profile of MSC therapy from a properly run program is favourable. The literature, across thousands of patients and years of follow-up, consistently shows MSC therapy as well-tolerated. Adverse events occur. Most are mild and self-limited. Serious events are rare and, in a hospital-based program, manageable.
The patient decision isn't whether MSC therapy is risky. It's which program is doing the work to manage the risk that does exist.
Questions to ask any program about adverse events.
- What's your most common adverse event, and what's the rate? A program that says "we've never had any" is either being dishonest or hasn't treated enough patients to encounter the predictable rare events.
- Do you have a documented SAE protocol? Yes/no question with a clear right answer.
- What's the medical infrastructure if something goes wrong during treatment? Hospital, on-site specialists, ICU access, transfer protocol to another facility?
- Will I receive my full medical record after treatment, including any adverse-event documentation? Patients have a right to their records.
- Will the clinic communicate with my US providers if a serious event occurs after I return home? Continuity of care across borders matters.
"Nothing has gone wrong" is a claim. "We're structured to handle it" is a system.
Most stem-cell treatments have no acute complications. The most common predictable event is mild flu-like symptoms in a subset of patients, resolving overnight. Direct-injection soreness is the body's intended response, not a complication. Serious adverse events are rare and well-characterised.
The protocol that makes those statements durable is the SAE infrastructure: hospital-based treatment, physician supervision throughout, structured observation, documented response procedures, continuity of records, and follow-up that catches problems before they escalate. The right question for any clinic isn't "have you ever had a problem?" It's "what's the system if you do?"
Predictable events, openly stated
Occasional mild flu-like reactions in IV patients, expected soreness after direct injection. Named, characterised, time-limited, not buried.
Rare events, hospital-managed
The categories of rare SAE are known. Each has a named protocol response. Hospital infrastructure converts response time from minutes-to-911 into seconds-down-the-hall.
Continuity, across borders
CoA, clinical record, and physician-to-physician access if a US provider needs to evaluate after return. The chart doesn't stop at the border.