Every medicine has side effects, and botulinum toxin is no exception. What matters clinically is knowing which effects are common and settle on their own, which are uncommon but treatable, and which are rare enough that they should never be presented as likely. This is the list our doctors work through before consent, without the promotional gloss.
The common ones
Bruising and swelling
A small bruise or a raised bump at an injection point is the single most likely effect. It usually fades within three to seven days. Risk rises with aspirin, clopidogrel, some supplements, alcohol in the days around treatment, and the week before a period. Cold compresses in the first few hours help, and make-up is fine once the tiny marks have closed.
Injection-site tenderness
Mild soreness or a small lump for a few hours is normal. It should not be massaged, because pressure in the first hours is exactly what we are trying to avoid.
Headache
A short-lived headache in the first 24 to 48 hours is recognised, particularly after frown-line treatment, and normally settles with ordinary pain relief. Persistent or severe headache after treatment should be reported rather than tolerated.
Less common, usually temporary, and manageable
Asymmetry
Faces are not symmetrical to begin with, and muscle response can differ slightly from one side to the other. Most asymmetry is subtle, noticed by you far more than by anyone else, and can often be balanced with a small, targeted adjustment at the two-week review.
Brow or eyelid heaviness (ptosis)
This is the complication patients fear most, and the one that separates experienced practice from optimistic practice. It happens when product reaches a neighbouring muscle and causes a temporary droop of the eyelid or brow. Published series report it in roughly one to five in a hundred frown treatments. It is temporary, typically resolving over two to twelve weeks, and specific prescription eye drops can improve the appearance while it settles. It is the main reason placement, anatomy and dose matter, and why a review appointment is not optional.
Expression that feels too tight
A brow that feels heavy, a forehead that will not move, or a look that reads as surprised are dosing and placement decisions rather than bad luck. They are the reason first treatments should be conservative.
Dry eye or a change in blinking
When treatment sits close to the muscle around the eye, some patients notice drier eyes or a change in how they blink for a few weeks. Lubricating drops usually help, and it settles as the effect wears off.
Lip flip: changes to smile and speech
A lip flip can alter how the upper lip moves when you smile, drink from a straw, or pronounce certain sounds. For most people it is a pleasant change. For a minority, it feels unnatural for the first few weeks.
Jaw treatment: temporary chewing fatigue
Masseter treatment, whether for jaw slimming or for clenching and grinding, can cause tiredness when chewing for a few weeks, particularly at higher doses. It is dose-related and usually mild.
The rare ones
These are uncommon enough that most patients will never encounter them, but they belong in an honest consent conversation.
- Infection at an injection site: redness, warmth, increasing pain or discharge.
- Allergic reaction: localised swelling or rash, and very rarely a more serious reaction requiring urgent medical attention.
- Temporary double vision, or difficulty fully closing an eye, when treatment is placed close to the eye.
- More widespread muscle weakness, which is rare at cosmetic doses but recognised.
- Antibody formation after repeated or frequent high-dose treatment, which can make future treatment less predictable.
What raises your individual risk
Risk is not the same for every face. It rises with higher doses, with treatment in anatomically delicate areas, with a first treatment where your response is unknown, with blood thinners and supplements that affect clotting, and with underlying neuromuscular conditions. Previous poor response, unusual anatomy, or a history of asymmetry all change the plan. None of this is a reason to avoid treatment, but all of it is a reason to be assessed properly before it.
If something does not feel right
- Take a clear photograph in natural light, front on and in animation, on the day you notice it.
- Contact the clinic that treated you directly, rather than waiting for your review.
- Do not massage, rub or apply heat to the area hoping to 'move' the product. It does not help and can make bruising worse.
- Attend your two-week review, when the full effect is visible and adjustments can be judged properly.
- Seek urgent medical help for difficulty breathing, swallowing or speaking, or for sudden widespread weakness. These are very rare and should never be managed by waiting for a clinic's opening hours.
What is not a side effect
Aesthetic medicine carries a great deal of folklore, in both directions. There is no evidence that cosmetic botulinum toxin causes cancer. It is not a permanent nerve poison: its effect is temporary because new nerve terminals regrow over weeks to months. Some laboratory work looks at distant effects of the molecule in experimental settings, which is why it is a prescribed medicine rather than a cosmetic, but that is not the same as clinical harm at approved cosmetic doses. Equally, 'natural' and 'gentle' are not safety guarantees: dose and technique are what matter.
How we reduce risk in practice
- An in-person assessment and a documented medical history before prescribing.
- A conservative first dose, with the option to refine at two weeks rather than over-treat on day one.
- Anatomy-led placement, especially around the brow and eye.
- A minimum interval of about three months between treatments, to reduce antibody risk and to let each result be assessed honestly.
- A two-week review as standard, with photographs and a written record.
- A clear route back to the clinical team if anything concerns you.
If you are weighing up treatment, the most useful next step is a proper conversation rather than a comparison of prices per unit. You can read about anti-wrinkle injections in Manchester, and about aftercare and what it is really based on.
This article is general information, not medical advice, and is not an advertisement for a prescription-only medicine. Side effects should be discussed with your prescriber before treatment.
