Iowa Code § 205.9: Prohibited sales.

It shall be unlawful for any person in this state to sell or deliver any poison to any person known to be of unsound mind or under the influence of intoxicants, and it shall likewise be unlawful for any person in this state to sell or deliver any poison enumerated in section 205.5 to any minor under sixteen years of age except upon a written order signed by some responsible person known to the person selling or delivering the same, which said written order shall contain all of the information required to be entered in the poison register under the provisions of section 205.6.