How do i stop a 4 years old child from sucking her thumb. is there any medicine out there?

Bedtime: I try to narrow the thumb sucking to nap or bedtime. I tell the child it is okay to suck the thumb in bed. By focusing on one time per day, the child feels there is still hope of not getting in trouble for the habit. Eventually, the nighttime habit will lessen too. Medicines, bandages and yelling do not seem to work well.

Thumb sucking: There is no medicine other than lubrication i.e. vaseline and positive reinforcement for not sucking the thumb (you look great when you don't have the thumb in your mouth!). In time, the need to do this will eliminate.

Thumb Sucking: A difficult habit to break, but continuation of the habit can have consequences in the development of the maxilla and mandible, as well as the position of the permanent teeth. https://www.webmd.com/parenting/features/9-ways-to-wean-a-child-off-thumb-sucking#1