**5. Early clinical experience with cannabis for the treatment of epilepsy**

The use of cannabis as a treatment for a variety of ailments in eastern and Mediterranean cultures over the last several millennium has been well documented [47]. The first description of the use of cannabis to treat seizures came from Dr. W. O'Shaugnessy who while working in India reported its successful use to treat seizures in an infant [48]. Following this, cannabis extracts became widely used throughout Europe and North America as an accepted treatment for epilepsy [49]. Following prohibition and with the introduction of other anticonvulsants, cannabis fell out of use as a treatment for epilepsy in western cultures.

During the mid-twentieth century, several reports on the effect of recreational cannabis consumption surfaced with contrasting effects. Several case reports described patients having decreased seizure frequency following the consumption of cannabis [50]. Cannabis consumption was also shown to be protective against first unprovoked seizures. In adult males who smoked cannabis in the last 90 days, the odds of having a first unprovoked seizure was 0.38 compared to adult males who never consumed cannabis [51]. Conversely, a patient with a history of epilepsy who had been seizure free for several months on medication was reported to have had an exacerbation of seizures following the consumption of cannabis [52].

In 1978, Mechoulam et al. reported their double blinded placebo-controlled study of CBD used as an add-on therapy in patients with refractory focal onset seizures. Of the four patients who took CBD two were seizure free for the 3 months of the study while another had partial improvement. None of the five patients who took placebo had any improvement in their seizures [53]. Cunha et al. reported the results of their study investigating the potential of CBD in patients with refractory temporal lobe epilepsy. In the first phase of the study, healthy adult volunteers were randomized to receive either placebo or CBD at 3 mg/kg/day for 30 days. Of 8 volunteers receiving CBD, 2 reported somnolence otherwise no adverse effects were reported. In the second phase, 15 adult patients with drug-resistant temporal lobe epilepsy were randomized to receive either placebo or CBD (up to 300 mg/day) for a period of 18 weeks in a double-blinded manner. Four of 8 patients dosed with CBD had complete improvement while three had partial improvement. No adverse effects were noted in patients given CBD [54].

Two further studies showed no significant difference in seizure reduction with the addition of CBD as an adjunctive therapy. However, in one study patients were given CBD at a dose of 300 mg/day and their plasma CBD levels were maintained at 20–30 ng/ml. Subsequently one participant who had no difference in their seizure frequency was placed on CBD at a higher dose of up to 1200 mg/day. CBD plasma levels were higher averaging 150 ng/ml. This patient had a significant decrease in their seizure frequency suggesting that higher doses of CBD (and higher plasma levels) were required for seizure control [55].
