Botox works by irreversibly binding to receptors that send nerve signals for muscles to contract. But, since your body makes new receptors and neurotransmitters all the time, each patient will have different lengths of effective paralysis. 2-6 months is the range; average is 3-4 months. But wait, there's more! To complicate the matter further, Botox (and Dysport, another company's botulinum toxin) is a labile protein, meaning it is sensitive to heat, excessive agitation, and time. Careful reconstitution, use while fresh, and keeping it refrigerated is essential. Beware offices or spas that advertise Botox days (especially if it's Friday)--they are simply trying to use up their reconsituted Botox so it won't sit over the weekend and lose effectiveness. Particularly beware of Monday morning Botox in such centers! Then there's the skill and accuracy of the injector. Since Botox works where it's placed, simply shooting in a blob of liquid Botox in the general vicinity of the target muscle is a waste (of your money)! The most experienced injectors are plastic surgeons who actually operate on the target muscles in patients having forehead or brow lifts, facelifts, and eyelid surgeries. In my humble opinion, non-surgeon doctors and nurses can become experienced Botox injectors over time without operating on these areas, but consider who is best trained and experienced in the anatomy of the treatment areas. Remember: the bitterness of poor quality remains long after the sweetness of low price is forgotten! Best wishes! Dr. Tholen