What Triggered My MG? Infection, Medication, Stress — or Bad Luck?

When myasthenia gravis (MG) seems to begin suddenly, it is natural to look backwards.

Was it the respiratory infection a few weeks earlier? A new antibiotic? An operation? Months of stress? Pregnancy? COVID-19? Or was the timing simply a coincidence?

Research gives a more complicated answer than any single explanation. Infections, certain medicines, stress, surgery and hormonal changes can worsen MG symptoms or coincide with their first noticeable appearance. But for most people, it is not possible to prove that one event caused autoimmune MG.

That distinction matters. A trigger for weakness is not necessarily the cause of the autoimmune disease itself.

TL;DR

• The exact event that starts autoimmune MG usually cannot be identified.
• Infections, stress, surgery and certain medicines are established triggers for worsening MG symptoms, but evidence that they cause new MG is much less certain.
• Some medicines are important exceptions: drugs such as D-penicillamine and some cancer immune checkpoint inhibitors have been associated with new-onset MG.
• In 30 UK MG conversations reviewed through the mama health app, recurring suspected triggers included respiratory infections, medicines, surgery, major stress, hormonal events, vaccination and no identifiable event at all.
• Looking at these shared themes can help you reflect on your own timeline and prepare more specific questions for a healthcare professional, but similarities cannot establish the cause of MG.

What does it actually mean to say something “triggered” MG?

A trigger may make MG weakness more noticeable without being the event that originally created the autoimmune process.

Autoimmune MG develops when the immune system produces antibodies that interfere with communication at the neuromuscular junction, where nerves signal muscles to contract. Acetylcholine receptor antibodies are the most common, while other forms involve proteins such as MuSK or LRP4.

You can read more about the different antibodies involved in myasthenia gravis.

Why that autoimmune response begins is still not completely understood. Genetics appear to influence susceptibility, but autoimmune MG is rarely inherited in a simple or predictable pattern.

This creates an important difference between three ideas:

• Cause: something shown to initiate the disease.
• Trigger: something that can worsen weakness or bring symptoms to attention.
• Timing: something that happened shortly before symptoms but may be unrelated.

For one individual, these can be difficult to separate.

A respiratory infection followed by double vision, for example, creates a convincing timeline. But timing alone cannot prove that the infection created MG.

What have people using mama health described before their MG became noticeable?

A qualitative review of MG conversations in the mama health app found several recurring explanations people considered when looking back at the start of their symptoms.

The conversations discussed suspected causes or triggers rather than medically confirmed causes. Recurring themes included:

• COVID-19 and other respiratory infections
• antibiotics and other medicines
• surgery or anaesthesia
• bereavement, work pressure and prolonged stress
• pregnancy, the postpartum period and other hormonal changes
• vaccination
• no obvious preceding event

Respiratory infection was the most recurring theme in this small set of conversations.

Seeing how others describe the weeks or months around their first symptoms can help someone remember details from their own timeline: when eyelid drooping began, whether double vision appeared after an infection, whether a medicine had recently changed, or whether weakness became more noticeable during an unusually demanding period.

mama health offers a place to record and reflect on experiences like these and see themes described by others. That can make an uncertain story easier to put into words and discuss during a medical appointment. It does not determine what caused MG.

Can an infection trigger myasthenia gravis?

Infections are well-established triggers for worsening MG symptoms, but evidence that an infection directly causes autoimmune MG is much less certain.

Respiratory infections are particularly relevant. Viral and bacterial illnesses can place additional demands on the body, and infection is a recognised precipitating factor for MG exacerbations and myasthenic crisis.

Research has also described MG beginning during or shortly after respiratory infections, including viral illnesses. Scientists have proposed several possible immune mechanisms, such as cross-reactivity between infectious agents and the body's own proteins.

However, these mechanisms remain hypotheses rather than proof that a specific virus directly caused MG in an individual.

COVID-19 illustrates the problem clearly. Cases of new MG following SARS-CoV-2 infection have been reported, and people using mama health have also described that sequence. But a diagnosis appearing after COVID-19 does not by itself demonstrate causation.

If an infection coincided with your earliest weakness, it is reasonable to include it when describing your timeline. It is less accurate to conclude that the infection definitely created the disease.

For more context on how weakness can appear and fluctuate, see how myasthenia gravis symptoms can present.

Can medication trigger or worsen MG?

Yes, some medicines can worsen myasthenic weakness, while a much smaller group has been associated with the development of new MG.

This distinction is important.

Several medicines can interfere with neuromuscular transmission and make weakness worse when MG already exists. Examples that appear on specialist caution lists include certain:

• fluoroquinolone, macrolide and aminoglycoside antibiotics
• beta-blockers
• antiarrhythmic medicines such as procainamide
• magnesium, particularly intravenous magnesium
• neuromuscular blocking drugs used during anaesthesia

This does not mean every medicine in these categories is automatically unsuitable for everyone with MG. The strength of evidence varies, and sometimes a medicine is medically necessary.

There are also rarer situations in which medication may be associated with new-onset MG, rather than simply worsening existing weakness. D-penicillamine has a particularly strong association. MG can also occur as a rare immune-related complication of cancer treatment with immune checkpoint inhibitors.

That is why a medication timeline can be useful. If weakness started after a new prescription, writing down the medicine, dose and timing can give a healthcare professional more context.

mama health also has a separate guide to medicines that may require caution with myasthenia gravis.

Can surgery or anaesthesia bring MG symptoms to the surface?

Surgery and some medicines used around anaesthesia can worsen MG weakness, although surgery itself is not usually considered the underlying cause of autoimmune MG.

Major procedures put physical stress on the body. In addition, people with MG can be particularly sensitive to some neuromuscular blocking medicines used during anaesthesia.

This may help explain why someone occasionally notices pronounced weakness during the days surrounding an operation.

It is therefore useful to distinguish between:

“My MG became noticeable after surgery”

and

“The surgery caused my MG.”

The first describes a timeline. The second makes a causal claim that usually cannot be established.

For someone who already knows they have MG, discussing the condition and current medicines with the surgical and anaesthetic team provides important context before a planned procedure.

Can severe stress trigger MG?

Stress can worsen MG symptoms, but research has not established psychological stress as a direct cause of autoimmune MG.

Stress appears repeatedly in personal accounts.

In the mama health conversations reviewed for this article, people described periods involving bereavement, relationship breakdown, intense work pressure, caring responsibilities and prolonged exhaustion around the time symptoms became noticeable.

Stress is also recognised by clinical sources as something that can make established MG symptoms worse.

What is much harder to determine is whether stress can initiate autoimmune MG.

The evidence does not currently allow that conclusion.

This distinction can be especially important when the first symptoms appear during an emotionally difficult period. Drooping eyelids, double vision, swallowing difficulty or fatigable muscle weakness should not automatically be explained away simply because stress is also present.

The emotional impact of trying to understand a new chronic condition can also be substantial. Our guide to MG and emotional wellbeing explores that side of living with the condition.

Can pregnancy or hormonal changes affect MG?

Pregnancy and the postpartum period can change the course of MG, but hormonal events do not provide a simple explanation for why autoimmune MG begins.

The relationship between pregnancy and MG varies considerably.

A 2026 systematic review covering thousands of pregnancies found that MG symptoms worsened during some pregnancies, particularly during the first trimester. The period after giving birth is also recognised as a time when worsening can occur.

Some conversations in the mama health app also connected first noticeable symptoms with pregnancy, the months after childbirth, menopause, HRT or changes in hormonal contraception.

The strength of the evidence is not equal across those experiences.

Evidence is much stronger for changes in MG during pregnancy and the postpartum period than it is for menopause, HRT or contraception as causes of MG onset.

A hormonal event can therefore be worth including in a personal timeline without assuming it explains why the autoimmune disease developed.

Can a vaccination trigger MG?

Current evidence does not show that routine vaccination is a common cause of myasthenia gravis.

Cases of MG beginning or worsening after vaccination have been reported, including after COVID-19 vaccination. Case reports are useful for identifying possible safety signals, but they cannot establish how often something occurs or prove causation.

Larger population data provide important context.

A population-based study of people with MG found negligible risk of severe MG exacerbation after COVID-19 vaccination, while COVID-19 infection itself was associated with substantially more serious outcomes.

This does not mean that every individual experience is identical.

Someone who noticed symptoms after vaccination can accurately describe that timing. The evidence simply does not support moving from “this happened afterwards” to “this definitely caused my MG.”

Questions about individual vaccination timing can be discussed with a healthcare professional, particularly when immunosuppressive medicines are involved.

What if there was no trigger at all?

Many people cannot identify any clear event before MG appeared.

That can feel unsatisfying because the brain naturally looks for a before-and-after explanation.

But autoimmune diseases do not always provide one.

Some people describe months of subtle symptoms before recognising that something was wrong. Others remember a seemingly abrupt first sign: one eyelid starting to droop, double vision appearing while driving, difficulty chewing by the end of a meal, or arms becoming unexpectedly weak.

There may be no infection, new medicine, operation or major life event to connect it to.

Not finding a trigger does not mean you overlooked something important. It may simply mean that no identifiable external event explains when the disease became noticeable.

Is thymoma different from an everyday MG trigger?

Yes. Thymoma has a recognised biological association with autoimmune MG and should not be grouped with everyday triggers such as stress or tiredness.

A thymoma is a tumour of the thymus gland. Around 10–15% of people with MG have a thymoma.

The thymus is involved in immune-system development, and abnormalities within the thymus can contribute to the autoimmune processes associated with MG.

This is one reason chest imaging is commonly included in the evaluation of MG.

However, most people with MG do not have a thymoma.

Our detailed guide explains how the thymus, thymoma and thymectomy relate to myasthenia gravis.

How can I make sense of my own MG timeline?

A timeline can help organise what happened without requiring you to decide what caused MG.

You might reflect on:

• when the first definite weakness appeared
• whether there were subtler symptoms beforehand
• recent respiratory or other infections
• medicines that were started, stopped or changed
• surgery or anaesthesia
• pregnancy or the postpartum period
• major physical or emotional stress
• whether symptoms varied with activity and rest

The goal is not to prove a cause yourself.

It is to turn a confusing period into a clearer sequence of events that can be discussed with a healthcare professional.

mama health can support this kind of reflection by helping organise experiences and questions in one place. Similar stories from others may also give you language for experiences that were difficult to describe. They should be viewed as context, not as evidence that the same factor caused your MG.

If you are still making sense of how MG was identified, see how myasthenia gravis is diagnosed and which tests may be used.

What could I ask at my next medical appointment?

Questions about your timeline can help turn “What caused this?” into topics a healthcare professional can actually explore with you.

Examples include:

• Could the infection I had around the time symptoms started have made existing weakness more noticeable?
• Could any medicine I was taking have affected neuromuscular transmission?
• Have my current medicines been reviewed for MG cautions?
• Has my thymus been assessed?
• Which MG antibodies have been tested?
• Does my symptom pattern provide any useful context about when the disease may have started?
• Are there situations I could discuss with you that might make my weakness worse?

These questions do not assume that one trigger is responsible. They help separate what is known from what remains uncertain.

When can worsening MG weakness become urgent?

Rapidly worsening breathing, swallowing or speaking weakness can be an emergency in MG and warrants urgent medical assessment.

Myasthenic crisis occurs when weakness significantly affects the muscles needed for breathing. Serious swallowing weakness can also create complications.

This is different from trying to identify what originally triggered MG. Immediate safety matters more than reconstructing the cause when severe weakness is developing.

So, what probably triggered my MG?

For most people, there is no scientifically defensible way to identify one event and say, “That caused my MG.”

An infection may have occurred first.

A medication may have intensified weakness.

An operation may have made previously subtle symptoms impossible to ignore.

Stress may have coincided with a difficult period of fluctuating weakness.

Pregnancy may have changed the disease course.

Or there may have been no recognisable trigger whatsoever.

The most useful distinction is between what may have changed your symptoms and what caused the autoimmune disease to exist in the first place. Research understands the first question much better than the second.

The 30 UK MG conversations reviewed through mama health show why this question matters. People repeatedly look for a turning point because a sudden diagnosis invites an explanation. Seeing similar uncertainties in other people's stories can make your own experience easier to describe, while medical research helps establish where those similarities should — and should not — be interpreted as evidence.

You may never get a definitive answer to “Why did MG start when it did?”

But you can still build a clearer picture of what happened, what seems to affect your weakness now, and what you would like to discuss at your next appointment.

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