When two or more drugs are taken at the same time (whether they are legal or illegal) they are likely to interact with one another, so that one drug changes the effects of the other. This means:
- one or both of them may become toxic
- their effects may be decreased or increased
Your age, weight, genes, general health and liver or kidney function will make a difference to the way the drugs work. However, there are some common interactions that many people experience.
Interactions between recreational drugs
Mixing drugs, or mixing drugs with alcohol, is always dangerous. The effects can be hard to predict, but there are some known interactions:
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Drugs taken together
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Interaction
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two or more depressants – e.g. heroin plus a benzodiazepine or alcohol
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the depressant effect will be increased, slowing your heart and breathing – this may be fatal
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two or more stimulants – e.g. cocaine plus ecstasy
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can cause your heart to race (and can be very frightening) – this may be fatal
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depressant(s) and stimulant(s)
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can put a strain on your heart – can be fatal
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cocaine and alcohol
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produces a substance called coca-ethylene, which is poisonous
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alcohol may suppress the effect of cocaine, so you may take more and overdose
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ecstasy and cannabis
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can make you anxious and paranoid
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heroin and cannabis
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very dangerous and easily fatal
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pregabalin
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can increase the euphoric effects of other drugs (such as opiates)
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Interactions between recreational drugs and prescribed medication
These are some of the known interactions between drugs and psychiatric medication.
Drugs may also interact with any other type of prescribed medicines, as well as those bought over the counter.
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Drugs taken together
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Interaction
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MAOI antidepressants with many other drugs
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can cause very dangerous effects, including very high blood pressure, chest pain, neck stiffness, rigid muscles, flushing, vomiting and severe headaches
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reversible MAOI (moclobemide) with stimulants
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may cause life-threatening effects, as above
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chlorpromazine with amphetamine
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the effect of both drugs may be reduced
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lithium with cocaine
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effect of cocaine reduced
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lithium with amphetamine
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effect of amphetamine blocked
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lithium with alcohol or ecstasy
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dehydration may cause lithium levels to become toxic
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carbamazepine with cocaine
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effect of cocaine reduced
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carbamazepine with methadone
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reduces methadone levels
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ketamine with depressants (sedatives)
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breathing reduced
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most antidepressants, antipsychotics and tranquillisers with alcohol
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first generation antipsychotics with ecstasy
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increases risk of movement disorders
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cannabis with clozapine and olanzapine (antipsychotics)
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reduces amount of antipsychotic in body
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citalopram (SSRI antidepressant) with cocaine
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may cause brain haemorrhage (bleeding), high blood pressure and risk of bleeding – this effect was reported in July 2016 and may also apply to other SSRI antidepressants.
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tobacco with clozapine and olanzapine
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smoking reduces the effect of clozapine and olanzapine, so your dose of these drugs will need to be adjusted if you stop or start smoking (this is an effect of the hydrocarbons in the smoke, rather than the nicotine)
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risperidone with cocaine
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reduces 'high' of cocaine
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This information was published in November 2016. We will revise it in 2019.
