1a. Histamine: C5H9N3
1b. 
1c. The amine functional group
2a. Antihistamine: C16H21N3
2b. The positions of the amine and imine groups in relation to each other are similar for both histamine and antihistamine which allows the antihistamines to compete with the histamines.
3. Physiological response: Morphine, amphetamine, oestrogen
Inhibit growth: Penicilin, aspirin, (Keflex) antibiotic
4a. Manufacturers can put labels on their supplements, talking about its health claims (what happens when you take the supplement and other food or food components) , its nutrient contents (how much nutrients the supplement can give), and its structure, describing how a product may affect the organic or the body.
4b. Somewhat. The Health Sciences Authority controls the flow of Chinese Proprietary Medicine into Singapore by issuing licence and testing of drugs before they are sold to the market.