Does cannabis interact with antidepressants or lithium?

Cannabis or marijuana is usually smoked and typically mixed with tobacco. It can interact with certain types of antidepressants, such as tricyclic antidepressants (TCAs), which share similar side effects.

Lithium is used to treat bipolar disorder, a condition where people can switch between depression and mania (extreme excitement and agitation). There is little evidence that people who use cannabis should normally not take lithium, but proper research is not available.

Types of antidepressants

There are four main groups of antidepressants:

  • tricyclic antidepressants (TCAs), such as amitriptyline, imipramine and dothiepin – both cannabis and TCAs can cause an abnormally fast heartbeat (tachycardia) and high blood pressure (hypertension). There is also a risk of other side effects such as confusion, restlessness, mood swings and hallucinations.
  • monoamine oxidase inhibitors (MAOIs), such as phenelzine – studies suggest that cannabis may affect the way these medicines work, but it is not clear what effect this may have on people.
  • newer antidepressants, such as mirtazapine, venlafaxine and reboxetine – there is no published research that has looked at taking these medicines and cannabis; the newer antidepressants should therefore not be taken with cannabis because of this lack of information.
  • selective serotonin reuptake inhibitors (SSRIs), such as fluoxetine, sertraline, paroxetine and citalopram – these may be a safer choice of antidepressant if you regularly use cannabis. However, there has not been any proper research on taking cannabis with SSRI antidepressants. Speak to your doctor.

Side effects of cannabis

It is not clear how often cannabis itself can cause depression, but research suggests that this can happen. It is therefore recommended that if you are depressed and you use cannabis regularly, you should try giving up and see if that helps.

Tachycardia, dizziness, anxiety, drowsiness, nausea and vomitingdifficulty sleeping and confusion are all possible side effects of cannabis. These side effects can also be caused by certain antidepressants, so using cannabis at the same time can make them worse.

If you have any concerns about the information above or need any help understanding it and relating it to your own situation, talk to your GP or pharmacist (chemist). You can also phone NHS 111.

Further information:

Page last reviewed: 10/05/2013

Next review due: 09/05/2015