UPDATE 2-Zynerba's stock on a high as cannabis-based drug succeeds in trial

(Adds details on cannabis-based drugs, background on U.S. cannabis laws, updates share price)

Sept 28 (Reuters) - Zynerba Pharmaceuticals Inc said on Thursday its cannabis-based gel met the main goal in a mid-stage study of patients with Fragile X syndrome, a genetic disorder that causes learning disabilities in adolescents and children.

The U.S. drug developer's shares, which are down 60 percent since the beginning of the year, climbed 71 percent in premarket trading to $10.60.

Zynerba's drug achieved the main goal in a mid-stage study of adolescents and children with Fragile X syndrome by improving the total score on a scale assessing anxiety, depression and other behavioral symptoms associated with the disorder, the company said.

Fragile X, an autism-spectrum disorder, affects 1 in 4,000 males and 1 in 8,000 females and has no approved treatment, Zynerba said.

Zynerba's treatment also improved aberrant behaviors associated with the disorder, such as temper tantrums, social avoidance, repetitive movements and hyperactivity.

The drug, ZYN002, is a cannabidiol (CBD) gel, which last month failed a mid-stage study testing the drug in patients with epilepsy.

Cannabidiols belong to a class of chemical compounds found in the cannabis plant, which differs from THC, a psychoactive chemical that is also found in the plant.

Under U.S. federal law, marijuana is considered a dangerous substance with no medicinal value, making additional approvals for marijuana-derived treatments necessary prior to launch.

While marijuana remains illegal under federal law, more than two dozen U.S. states have legalized marijuana for medical or recreational purposes.

Zynerba said it expects to meet with the U.S. Food and Drug Administration in the first half of 2018 as it seeks to conduct another key, mid-stage study.

British drugmaker GW Pharmaceuticals' Epidiolex, which is also derived from CBD, successfully treated children with epilepsy in a late-stage trial last year. The company is expected to file a U.S. marketing application later this year. (Reporting by Manas Mishra in Bengaluru; Editing by Sai Sachin Ravikumar)