Dr. Mark Youssef, one of the best Botox doctors in Los Angeles, explains the specific parameters that a doctor or medical practitioner uses in determining the optimal amount of Botox needed. The number of units used for each patient varies and  is generally based on: - How strong the patient’s muscles are - How broad the muscles are - How tall their forehead is - How thick their muscles are - Whether they are male or a female All of these factors are considered when determining the exact amount of Botox a patient will need.