A nicotine booster or nicotine shot is a 10ml bottle of flavour-neutral liquid that is enriched with 18 to 20mg of nicotine. The shots are added to the nicotine-free liquids in large format to achieve the desired nicotine content.
Due to the current European regulation of e-cigarettes, liquids and liquid flavours, the maximum content of nicotine-containing products is limited to 10ml. A practical alternative to the small vials is the so-called shortfill format, which usually comes with a capacity of 60ml. This 60ml bottle contains 50ml of highly aromatic liquid, while 10ml remain free to add a nicotine shot directly in the bottle.
The dosage always remains the same: 50ml of liquid plus a 10ml nicotine shot with 20mg nicotine result in a nicotine content of 3mg. With 2 shots you reach 6mg, and so on. At Freevap you will find a table in every product description of a nicotine shot, with which you can check the necessary dosage in case of doubt. By the way, depending on the empty volume in the bottle, you may need to add a larger container when using more than one shot.