Make a hot tea. When it cools use it as a final hair rinse for dandruff.
According to Ye Olde Wikipedia Rosemary may have a noticeable effect on the brain, improving memory but slowing recall. Epileptics should however avoid it.
If you are talking about contraindications for rosemary, add pregnancy to the list. Included below is a link for a whole list of herbs contraindicated during pregnancy.
Here is a link that might be useful: Pregancy - Herb Safety Chart
Since its on the Use in moderation list I would imagine that use as a topical dandruff control measure would not be contraindicated.
Thanks fatamorgana. Glad you posted the info.
Rosemary is a circulatory stimulant (the reason its contraindicated in pregnancy) with an affinity for the head. My first and favorite go to remedy for simple headache. It also increases alertness so is good for students and those doing tedious mental work.