Are there certain medications or supplements you recommend for hyperfocus in someone with inattentive adhd. are there any that can make it worse?

Nothing: Replaces a face to face consultation with a psychiatrist to evaluate, rule out any medical conditions &/or contra-indications, diagnose and treat someone with adhd, inattentive type. To give you some advice without clinical exam would be unethical. Hope you are not too disappointed by my answer. Best wishes.

The underlying cause: Of adhd-inattentive type is the same as that of other types. Because Dopamine & norepinephrine systems are impaired differently in individuals with adhd, reflective of the number of candidate gene "combos"for adhd, trials of stimulant &/or non-stimulant medication are started low & titrated for optimal effect. Within a decade, genetic testing should be available clinically to direct med choices.