The present invention relates to the use of cannabidiol (CBD) in the treatment of patients with childhood-onset epilepsy who are concurrently taking immunosuppressant drugs. In particular the immunosuppressant drug is a calcineurin inhibitor. More particularly the immunosuppressant drug is tacrolimus. Where the CBD is used in combination with an immunosuppressant drug, caution should be taken. For example, the dose of either the CBD and / or the immunosuppressant drug may be required to be reduced. Moreover, the patient may need to be monitored for side effects of said drug-drug interaction. Preferably the CBD used is in the form of a highly purified extract of cannabis such that the CBD is present at greater than 98% of the total extract (w/w) and the other components of the extract are characterised. In particular the cannabinoid tetrahydrocannabinol (THC) has been substantially removed, to a level of not more than 0.15% (w/w) and the propyl analogue of CBD, cannabidivarin, (CBDV) is present in amounts of up to 1%. Alternatively, the CBD may be a synthetically produced CBD.
