What side effects can Botox cause?
Most readers in Mamaroneck and Larchmont who ask about Botox side effects are sorting two piles. One pile is what can be waited out. The other is what means a phone call today.
The common list
The Cleveland Clinic lists the most common side effects as headache, bruising and numbness at the injection site, temporary eyelid droop (ptosis), eyebrow droop (eyebrow ptosis), eyebrow asymmetry and nausea.

How to read it
Of those, the droop and the asymmetry change how your face looks. Describe those to the clinic that treated you rather than waiting to see whether you imagined them.
Do not try to fix an uneven result by pressing or massaging the area. Leave it alone until you have spoken to the clinic.
What a source can and cannot tell you
A list like this tells you what is commonly reported. It cannot tell you what is happening in your own face. That takes a clinician who has seen it. Before you leave the appointment, whether in Harrison, Rye or White Plains, note the number to call if something changes.
Further reading
The American Society of Plastic Surgeons page on botulinum toxin and a MedlinePlus drug information entry on daxibotulinumtoxinA-lanm are two starting points. Two papers go deeper, one on clinical uses of botulinum neurotoxins and their limitations and one a comprehensive review of botulinum toxin therapy.
The follow-up question
Once side effects are clear, people ask how long Botox lasts. Ask that at the visit too.