How does the state not get involved in forcing medical treatment on an adult?

Even if a relative is designated as a guardian, if the person refuses treatment what happens?

Forcing an unwilling adult to regularly take medication is not a simple thing to do and in many cases will require physical restraint or violence (or the threats thereof).

Even getting a young child to take medication can be challenging (try getting a 5 year old to go through a 2 week antibiotic treatment w a liquid antibiotic that tastes bad...).