What does "run to the damn head" mean？
A simple Benzedrine capsule was all that was needed to keep a man sharp during the short haul, and it didn't keep you running to the damn head every ten minutes.
Question: It means that the medicine will keep one excited in a short time and what?

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If the speaker is on a boat, 'head' means 'toilet'.

He's referring to the fact that other ways of keeping alert mean that you have to go to the toilet a lot. If you drink a lot of coffee, you may need  to rush to the toilet quite often. Caffeine-based drugs may also upset your stomach. He doesn't have this problem with Benzedrine.

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Head is strictly a military term.

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no, the word "head" or "heads" mean the toilet