の before 後, mandatory or not?


In a textbook I saw this sentence talking about drugs:

> 一日に二回朝ご飯と晩ご飯後に飲んでください。

Is there a missing "の" between 晩ご飯 and 後? Is it ok to remove this particle in
casual speech?




Generally, the following are possible combinations.

  * Noun + [後]{ご} e.g. [食事後]{しょくじご}
  * Noun + の[後]{あと} e.g. 食事の[後]{あと}
  * Verb phrase + [後]{あと} e.g. 食事した[後]{あと}

it depends on each word which of 後 and の後 sounds more natural. 食事後/食事の後 sound
equally natural to me, but 晩ご飯[後]{ご} does not sound quite idiomatic, at least
less so than 夕食[後]{ご}.

Roughly speaking, it should be more common to use [後]{ご} with 漢語 and の[後]{あと}
with 和語 while there are many that can go with both (like 食事). Also due to this
nature, [後]{ご} sounds more formal (and thus appropriate for an instruction of
medicine).

