The effect of Botox should last at least 3 to 4 months -- but will last for longer or shorter periods in approximately 10 percent of the population. These differences in length of effect can be accounted for by differences in 3 factors: 1.) the quality of the product itself, 2.) the injector's dilution and injection techniques and 3.) the patient's genetic makeup and physical activities following injection.Product factors that can effect longevity:1. Damaged Botox molecules: Occasionally, and very rarely, there is a "bad batch" of Botox that just isn't as effective as it should be. This can happen whenever there is an error in the purifying process where the Botox molecule becomes damaged and therefore less effective. The only way your injector is going to figure out if this is the case with a certain batch is if people like you report instances when they believe their Botox has not lasted as long as it should, or as long as it usually does.2. Different forms of the molecule: There are other products on the market that work very much the same way as Botox (as a class, they are all called "neuromodulators"). The brand names of these other products are "Dysport" and "Xeomin". Although these are close to being composed of the same molecules as Botox, the slight differences between these forms can make a significant difference in effect or longevity. However this difference is determined primarily by individual patient factors (see below).Patient factors that can effect longevity:1. Individual differences in metabolism: Since Botox is a molecule with structural components found in nature, each person's body metabolizes it, but does so at different rates. Hence some people get rid of the Botox and it's effect sooner than others. Some people are even immune to or can develop an immunity to it's effect -- and therefore get little or no effect. These metabolic factors are genetically determined. Therefore you can't do anything about this except try another similar (but different enough) product like Dysport or Xeomin2. Individual sensitivities to the different neuromodulators: Dysport and Xeomin are essentially the same as Botox, with minor differences in their molecular structure. However these minor differences may make a big difference in how long each product lasts. So if you aren't getting at least 3 to 4 months effect from your injections, then switch to and try one of these other neuromodulator products. They may last longer AND you might find that they are less expensive.3. Use of treated muscles immediately following injection: If the treated muscles ARE used repeatedly during the first 2 to 4 hours following injection, it's possible that the Botox will have a BETTER and LONGER lasting effect. This is, as far as I know, not a certainty, but it certainly will not hurt to do this for a while following your injections, just in case.Injector factors that can effect longevity:1. Number of Botox "units" injected: Ultimately, what is most important when determining the worth of your Botox treatment, and the expected effect from it, is HOW MANY UNITS ARE BEING INJECTED. Don't just get an "area" treated without asking how many units are being used. Less units may give you the same initial result, but it just won't last as long.2. Dishonesty: Depending on the volume of water (actually "saline") that is used to reconstitute the Botox powder, there can be a different number of units of Botox molecules in the same volume water -- and each injector is free to add as much saline as they want. So just paying attention to how much fluid is being injected really tells you nothing. Therefore, you really can't be certain of how many units you are actually getting in a treatment unless you personally watch the injector reconstitute the Botox, then do the dilution calculations in your head, then pay close attention to how much volume is being injected. Some profit-hungry and unscrupulous operations will take advantage of your inability to tell how many units are actually being given by simply lying about it, and giving you fewer than they are charging you for. If you go to or come from another clinic and you were getting better longevity from the same number of units, chances are that the Botox was being over-diluted at the "bad" clinic.In any case, I wouldn't assume anything unless you have had a bad experience at the same clinic more than once. If you do, then you know it's NOT the product that's the problem; It's either you or the injector. The next step is to go to another clinic and see if you get the same short results WHEN USING THE SAME NUMBER OF UNITS. If you do, then it's an injector dilution problem. If you get the same bad results at any clinic, then your individual reaction to Botox is the problem and you should try one of the other products (Dysport or Xeomin).This is kind of a long-winded answer, but it's not an easy answer for each individual to figure out since any of these factors can be the cause or at least contribute to a shorter duration of Botox effect.