Botox injections work by interrupting nerve impulses to the muscles used when a person squints or frowns. When these muscles are relaxed, fine lines and wrinkles smooth out. The smoothing effect last up to 4 months. It could take a couple of weeks for Botox to kick in the first time it is done. The next shots would kick in after a couple of days and would last longer. Botox injections could last up to 4 months and after being in a relaxed state for a long time, the muscles restrain themselves to stay that way. If it is used early, mainly in the 30s and 40s, it can prevent wrinkles from setting in later in life.
Botox injections are often given in low doses of 25 to 75 units, which isn’t considered toxic. A deadly dose is about 3,000 units. Possible side effects of Botox include a small amount of bruising that would last for a few days, headaches, and strange feelings of heaviness. A person could have an uneven brow or a droopy lid if the wrong muscle is injected or unequal amounts are used on each side of the face.