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 with cannabis.

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 to suggest that people who use cannabis should normally not take lithium, but this has not been properly researched.

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. There is a risk that using cannabis whilst you are on any of these medicines could lead to problems such as tachycardia, even if you do not already have a heart condition. Speak to your doctor about this if you need advice.
• Monoamine oxidase inhibitors (MAOIs), such as phenelzine – it is not clear what effect this may have on people. If you need advice about taking cannabis with medicines in this class, speak to your doctor about this.
• Newer antidepressants, such as mirtazapine, venlafaxine and reboxetine – there is no published research that has looked at taking these medicines and cannabis. Speak to your GP if you have any concerns.
• Selective serotonin reuptake inhibitors (SSRIs), such as fluoxetine, sertraline, paroxetine and citalopram – there has not been any proper research on taking cannabis with SSRI antidepressants, so you should speak to your doctor about this.

Side effects of cannabis

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

Tachycardia, dizziness, anxiety, drowsiness, nausea and vomiting, difficulty 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. You can also phone NHS 111 or Talk to Frank, a friendly confidential drugs helpline on 0300 123 6600.

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