Does cannabis interact with antidepressants or lithium?

Cannabis and antidepressants

Cannabis or marijuana can interact with 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's also a risk of other side effects, such as confusion, restlessness, mood swings and hallucinations. 

There's a risk that using cannabis while you're on any of these medicines could lead to problems such as tachycardia, even if you don't already have a heart condition. 

Little research has been done into the interaction of cannabis with other types of antidepressants, such as SSRIs.

Cannabis and lithium

Lithium is used to treat bipolar disorder, a condition where people can switch between depression and extreme excitement and agitation (mania).

There's little evidence to suggest that people who use cannabis should normally not take lithium, but this hasn't been properly researched.

Side effects of cannabis

It's not clear how often cannabis itself can cause anxiety or depression, but research suggests this can happen.

It's therefore recommended that if you're anxious or 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.

Getting advice

If you have any concerns about the medicines you're taking, 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.

Further information:

Page last reviewed: 12/05/2015

Next review due: 12/05/2018