Can someone with a non-immigrant O visa get an extension due to medical treatment in Chiang Mai?

A person with a Non-Immigrant O visa is inquiring about the possibility of extending their visa due to a medical condition requiring ongoing treatment. However, a commenter advises that a hospital letter confirming the need for further injections is insufficient; instead, a letter must indicate that the person is unfit to travel. Without proper justification for not leaving the country, the individual may need to exit Thailand when the visa expires.