Final answer:
Supplementary words enclosed in parentheses in the ICD-10-CM codebook provide additional information that can clarify the meaning of the code.
Step-by-step explanation:
In the ICD-10-CM codebook, supplementary words enclosed in parentheses have the effect of providing additional information that can help clarify the meaning of the code. These words are not mandatory for coding, but they can provide context or further specification. For example, in the code J45.901 (Asthma, uncomplicated), the word "uncomplicated" in parentheses provides extra information about the type of asthma being coded.