Medical Chest on board is to be strictlly in accordance with Flag Requirements.

SO, Need to refer Flag State Requirements Booklet available onboard to ensure Correct Medicines and Medical Equipments on board. 

Apart from flag state requirements, sometimes the company also has their requirements for the medicines to be carried on board.

The first reference to be followed is the SMS manual of the ships. The requirement for medicines is usually listed in the Health, Safety, and Environment (HSE) manual provided on the ships by the company as part of the ISM code.

The HSE manual may specify the exact quantity of the medicines to be maintained on board or it may just have a statement where it asks to refer a publication such as "International medical guide for ships".

So the first thing that you should refer is the SMS manuals provided on the ship.