this worked on a cousin of mine-its also a nail-biting detterent. paint the nail of the thumbs (you can also coat the thumbs too) in tabasco sauce or something else really spicy or disgusting tasting. Some chemists sell special non toxic nail polish that tastes foul for this purpose too. With my cousin, it only worked if you did it while he was asleep because then he had no idea why it tasted so yucky. His thumbnails were painted every night after he was asleep and the taste soon put him right off sucking. It is also good to stop it early as it can have very bad consequences like buck teeth etc. which then require very expensive orthodontic work!!! good luck!!!

Hi,
the tabasco sauce is a good idea, but it didn't work on me when I was a child, I am 28 years old ( and still suck my thumb when I am tired) and started sucking my thumb when I was 3 1/2 years old, my parents have literally tried everything. They spent so much time telling me to get my thumb out of my mouth that I think it caused me to suck on it more. If you can't get the tabasco sauce or the nasty tasting polish to work, give your son a couple of weeks where you don't draw attention to the fact that he is sucking his thumb and he might stop on his own. When my kids started I just let them be and they stopped on their own. Good Luck!!