Side Effects after Botulinum Toxin: Drooping Eyelid, Asymmetry, Headache and What to Do

Why do side effects occur after botulinum toxin?

Botulinum toxin is a prescription medicine that temporarily reduces the contraction of the muscle into which it is injected. Most side effects have one of two causes: the needle itself (the prick, minor bleeding, swelling) and the medicine also affecting a neighbouring muscle beyond the targeted one.

Effects in the second group, such as a drooping eyelid, can last for as long as the medicine is active. The good news is that the effect of botulinum toxin is not permanent. As the nerve endings form new connections over time, the unwanted effect also disappears. For the basics of the treatment, see our article “Botulinum Toxin”.

Which side effects are considered normal?

The following are common, usually mild and pass on their own:

• Redness, small bumps and mild swelling at the injection points: these usually go down within hours.
• Tenderness or a mild stinging sensation: this is usually short-lived.
• Small bruises: these usually fade within a few days to a week. For details, see our article “Bruising and Swelling”.
• Mild headache: this may occur in the first days, especially after treatments to the forehead and between the brows, and mostly passes on its own.

If you want to take a painkiller for a headache, ask your physician which medicine is suitable for you. A headache that is severe, starts suddenly or keeps getting worse, however, is not the expected picture; you should consult a physician.

Why does a drooping eyelid (ptosis) occur, and how long does it last?

A drooping eyelid can occur when the medicine reaches the muscle that lifts the eyelid from the forehead or the area between the brows. It is usually on one side and noticed in the days after the treatment; the eyelid sits lower than usual and the eye may look smaller.

This is temporary, but it can last a few weeks. How long it lasts depends on the amount of medicine that reached the affected muscle and on individual differences. If you notice a drooping eyelid, inform the physician who performed the treatment. Your physician will assess the situation and, if appropriate, may recommend prescription eye drops that can help lift the eyelid slightly for a while. Do not use these drops on your own.

If a drooping eyelid comes with double vision, difficulty swallowing or slurred speech, it may not be just a local side effect. In that case, call 112 without waiting.

Drooping brows, an over-raised brow (“Spock brow”) and asymmetry

The forehead muscle lifts the eyebrows. If this muscle relaxes too much, the brows may sit lower than normal and a feeling of heaviness may develop above the eyes. This may be more noticeable in people whose brows are already low or who have excess eyelid skin.

The opposite can also happen: if the middle part of the forehead muscle relaxes while its outer edges keep working, the outer end of the brow lifts into a peak. This look is popularly known as a “Spock brow”. Slight differences between the two sides, that is, asymmetry, may also be seen, because the two halves of the face and the strength of the muscles are never exactly the same.

An over-raised brow or asymmetry is usually assessed once the full effect has settled, generally at around two weeks. If your physician considers it necessary, they may suggest a small top-up treatment to restore balance. With drooping brows, however, an extra injection is not always suitable, and often the approach is to wait for the effect to wear off.

An uneven smile and effects around the mouth

After treatments to the lower face, such as around the mouth, the chin and the neck, the two sides of the lips may move differently when you smile, and drinking through a straw or making certain sounds may be harder for a while. Because the muscles in this area are involved in functions such as speaking and eating, the effects may be more noticeable.

These effects are also temporary and improve as the medicine wears off. Your physician will assess the situation; in some cases balance can be restored with a small treatment on the other side, while in others waiting is the most appropriate approach.

Dry eyes and side effects around the eyes

After treatments for lines at the outer corners of the eyes, dryness, stinging or watering of the eyes, or difficulty closing the eyelid fully, may rarely occur. This may be linked to the eyelid muscle or the tear system being temporarily affected.

If you notice dry eyes or discomfort, inform your physician; they can advise you on suitable eye drops or measures to protect the eye. If you have eye pain, redness or a change in vision, you should be assessed without delay.

Rare but serious: when is spread of the medicine to distant areas an emergency?

The U.S. Food and Drug Administration (FDA) has added a boxed warning to the prescribing information of botulinum toxin products: the effect of the medicine can spread to muscles far from the injection site. This spread can appear hours or even weeks after the treatment. This picture is very rare; however, when it occurs it can be life-threatening.

When you go to the emergency department, say that you have had botulinum toxin, and when and where it was done. Such severe conditions may require monitoring and supportive treatment in hospital; the hospital team decides on the treatment. For signs of an allergic reaction, see also our article “Allergic Reactions in Aesthetic Treatments”.

When do side effects start, and when do they pass?

The timing of side effects helps you understand which ones are due to the needle and which to the medicine itself. The framework below is general; timings vary from person to person.

• Day of treatment: redness, small bumps and mild swelling may appear at the injection site; these usually go down within hours.
• First days: small bruises may become visible and a mild headache may occur. Bruises usually fade within a few days to a week.
• The days when the effect starts: the medicine starts to work within a few days. Muscle-related effects such as a drooping eyelid or brow, asymmetry and an uneven smile are usually noticed during this period.
• Around two weeks: the full effect has usually settled. Asymmetry or an over-raised brow can be assessed more reliably at this point.
• The following weeks and months: muscle-related unwanted effects improve as the medicine wears off. In most people the effect lasts about 3–4 months; unwanted effects often decrease markedly before then.

What can your physician do?

When you notice a side effect, your physician will first examine you and assess whether the symptom is related to the medicine, the needle or another cause. Depending on the situation, they may then recommend one or more of the following:

• Waiting and monitoring: many effects improve on their own as the medicine wears off.
• A balancing treatment: for asymmetry or an over-raised brow, a small top-up treatment if considered appropriate.
• Supportive treatments: suitable eye drops or protective measures for a drooping eyelid or dry eyes.
• Referral: for symptoms related to the eyes, the nervous system or allergy, referral to the relevant specialty or to the emergency department.

These decisions are individual and require an examination. Only the physician who assesses you can decide on the right approach for you.

Normal, consult your physician, or emergency?

Whenever you are unsure, call the physician who performed the treatment. This table is for general information and does not replace an examination.

What can you do at home, and what should you avoid?

• Follow the aftercare instructions your physician gave you after the treatment: do not rub, massage or press on the area.
• Avoid strenuous exercise in the first hours; avoid anything that puts pressure on the area and lying face down for as long as your physician recommends.
• Note any change you notice with the date and a photo; this makes your physician’s assessment easier.

Do not do the following:

• Do not massage the area to correct a drooping eyelid or brow; this may increase the spread of the medicine.
• Do not start prescription eye drops, painkillers or other medicines on your own.
• Do not have extra injections elsewhere shortly afterwards to correct asymmetry.
• Do not try methods suggested on social media.

For general aftercare principles, our article “Aftercare Following Medical Aesthetic Procedures” can be a useful guide.

How can side effects of botulinum toxin be prevented?

Side effects can never be eliminated completely; the treatment is not risk-free. However, the following steps can help reduce the risk.

To reduce the risk:

• Have the treatment done by a physician who knows facial anatomy and complication management, in a licensed healthcare facility.
• At the consultation, describe the position of your brows, any eyelid complaints and any side effects you have had before.
• Mention any muscle or neuromuscular diseases, any history of swallowing or breathing problems, and all the medicines you take.
• Make sure the product to be used is licensed; ask to see the box and the batch number.
• Follow the aftercare instructions and do not skip the follow-up appointment.
• If you have an important event, plan the treatment well in advance.

The risk of counterfeit products: why is it a separate danger?

Treatments carried out in places that are not healthcare facilities, such as homes or beauty salons, and with products obtained online carry serious risks. In the USA in 2024, illnesses with drooping eyelids, difficulty swallowing, shortness of breath and muscle weakness were reported after treatments carried out outside healthcare facilities by unlicensed people with products believed to be counterfeit; some people were treated in intensive care.

With counterfeit products or products of unknown origin, the content and amount are unknown, and if a problem occurs it is impossible to know what you are dealing with. For details, see our article “Counterfeit Products and Unlicensed Treatments”.

An honest note on the limits of the evidence

How often side effects occur and how long they last vary depending on the product used, the dose, the treatment area and the person. Published studies report different rates; for this reason we do not give exact percentages in this article. The most reliable information for you is the assessment of the physician who examines you.