What is the difference between milligrams (mg) and millilitres (mL)?

Milligrams (mg) measure weight, and Millilitres (ml) measure volume of liquid.

The part of the word 'Milli' comes from the latin mille, which means one thousand. There are 1,000 milligrams in a gram, and 1,000 millilitres in a litre of liquid.

Often people will tell you how much medicine they have taken in Millilitres, but the amount of liquid doesn't tell you anything much, unless you know how much the drug dissolved in the liquid weighed... it is the weight of the drug that is the actual dose.

For some medicines, such as methadone mixture, where the strength is usually 1mg (weight) per 1 ml (volume) the number for the dose and volume are the same, but as drugs (including methadone) come in different strengths it is good practice to always only talk about the dose using the weight - milligrams.

To prevent mistakes, and the L being mistaken for a 1, millilitres is usually abbreviated to mL.

E cigarettes, for example, sometimes have the nicotine dose expressed as mg/mL or milligrams per ml.

The 'high strength' refills contain 30mg/mL, this means that in every 1mL of intellicig e-cigarette refill liquid there is 30mg of nicotine. Drugs, of course, have their effect at different doses, so what is 'high strength' in one drug may have no effect with another drug, so the dose alone doesn't tell you much, unless you know how much of the drug is required to have an effect.

The high strength e-cigarettes, for example, have the effect of reducing cravings to smoke considerably, and many people find them helpful


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