Stiff neck after Botox: why, how long and what to do

After a botulinum toxin injection in the neck or along the jaw, some people describe a neck that feels stiff, heavy, or that tires quickly when they hold up their head or lift it while lying down. This is one of the possible neck problems after a botulinum toxin injection. In most cases it is a passing muscle weakness, bothersome, that disappears with the effect of the product. The first thing to check straight away: is there any difficulty swallowing, speaking or breathing? If so, this is no longer a simple stiff neck, and you must call emergency services (15 or 112 in France, or your local emergency number).

Why does the neck become stiff or weak?

In the neck, botulinum toxin is mainly injected into the platysma, the very thin, broad muscle just under the skin that forms vertical cords when it contracts. This use has no aesthetic indication in the French product labels; in the United States, a type A toxin is approved for moderate to severe platysma bands¹.

The intended effect is to weaken this muscle. But the US label points out that weakness can also affect neighbouring muscles, through spread of the toxin¹, and that botulinum toxin can weaken neck muscles that help with breathing¹. The French labels likewise describe effects linked to the toxin spreading away from the injection site^2,3. An expert consensus on the lower face stresses that injections into the lower part of the platysma bring no benefit and can only increase the risk of complications⁶.

In practice, this effect seems rare. In a placebo-controlled phase 3 trial on platysma bands, no case of muscle weakness or difficulty swallowing was reported⁵. In a review of studies on the lower face and neck, a single patient had mild weakness of the neck muscles⁴. These figures do not allow the frequency in everyday practice to be estimated precisely.

How soon after the injection does it appear?

Side effects of botulinum toxin usually appear within the first week after the injection^1,2. The weakness sets in gradually, at the pace of the product’s effect. A problem that appears later is still possible: the US label states that effects linked to spread of the toxin have been reported from hours to weeks after the injection¹.

How long does it last?

It lasts at most as long as the effect of the toxin injected, and often less. In the review mentioned above, the mild neck weakness lasted about two weeks⁴. The US label states, however, that side effects, although often transient, can last several months or longer¹. To understand what the product’s duration of action depends on, see the page about how long botulinum toxin lasts.

Is it reversible?

Yes. The effect of the toxin on the muscle is temporary: transmission between nerve and muscle is restored, first through small new nerve sprouts, then by the return of the original nerve ending⁷. The neck gradually regains its strength as the effect wears off.

Is there a treatment?

No treatment speeds up the disappearance of the toxin’s effect. Care consists of checking that this really is weakness linked to the injection, ruling out any effect on swallowing or breathing, then waiting for recovery. Any comfort measures are discussed with the doctor.

What should you avoid?

• Do not ask for another injection to "compensate": muscle weakness can be made worse by another toxin given before the effect of the previous one has worn off^1,3.
• Do not take a muscle relaxant or start a new treatment without talking to a doctor: the US label notes that some medicines can strengthen the effect of the toxin¹.
• Do not dismiss difficulty swallowing, even mild, as part of the stiffness.

When should you see a doctor?

Report a stiff or weak neck to the doctor who performed the injection, noting the date of the session, the areas treated and the day the problem appeared. Call emergency services without waiting (15 or 112 in France, or your local emergency number) if the stiffness comes with any of the signs below: the labels ask for immediate medical attention in case of swallowing, speech or breathing problems^2,3,8.

Difficulty swallowing is covered in detail on the page about difficulty swallowing after an injection. If the problem mainly affects the lower face and the lips, see the page on the stiff chin after an injection.