Polydrug Use: Factsheet

Mixing drugs or taking one drug when under the influence of another drug is known as polydrug use. Combining drugs in this way carries extra risks and can be extremely dangerous. The more drugs a person takes (or is affected by) at a time, the more chance there is of something going wrong.

An example of polydrug use would be smoking cannabis after drinking alcohol. Mixing alcohol with drinks that contain caffeine is another example.

The effect of mixing drugs depends on which drugs are mixed together. The effects of one drug are hard to predict and are affected by: 

• The drug itself (e.g. its purity, amount used, frequency of use, how the drug is used, whether the drug has been cut, or mixed with another drug);
• The person who is using the drug (e.g. their mood, expectations, personality and individual characteristics);
• The setting (e.g. where the person is, the people they are with).

Using more than one drug at a time makes the effects even more unpredictable. On top of all the factors listed above, the effect of mixing drugs depends on which drugs are mixed together. Combining drugs that have the same physical effects (e.g. two or more stimulants, or two or more depressants) is especially dangerous. This is because it increases the impact on the normal functioning of the brain and body.

Below are some possible effects of combining different combinations of drug types:

This factsheet was developed following expert review by researchers at the Matilda Centre for Research in Mental Health and Substance Use at the University of Sydney, the National Drug & Alcohol Research Centre at the University of New South Wales, and the National Drug Research Institute at Curtin University.

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