My son is 8 yrs old and was on Strattera. He also chewed on and licked his lips constantly, which drove me absolutely nuts, due to the fact that he also has "Atopical Dermatitis" so his skin is always chapped anyway.
Yes, such tics involving facial muscles and oral motor behavior are not an uncommon side effect of treatment with psychostimulants. Whether to persist with the treatment depends on several factors, including the severity of the ADHD symptoms and how much they interfere with normal functioning, along with the severity of the involuntary muscle movements. Change in dose or change to another stimulant are possible, as well as change to a non-stimulany treatment such as Strattera.