The ruling was made in the Higher Regional Court of Frankfurt, in a case against an anti-hangover drink-maker.
The judge said hangovers are an illness because they consist of small or temporary changes to the body's normal state.
Therefore, food products, including drinks, cannot be marketed as being able to prevent or treat illness.
The ruling occurred just in time for the nation's legendary Oktoberfest, which officially begins on the last Saturday of September.