Baclofen followed by Placebo

Placebo followed by Baclofen

Group A will be given 13 weeks of oral baclofen followed by a 2-week non-treatment (washout) period, and then 13 weeks of oral placebo.

For participants who with weight under 15 Kg at the time of enrolment, the initial oral baclofen dose will be 2.5 mg daily, increasing weekly over a 7-week period to 10 mg three times a day, and will be continued at that dose for the following 5 weeks.

For those participants who will be over 15 Kg at the time of enrollment, the starting oral baclofen dose will be 5 mg daily, increasing over a 9-week period to 20 mg three times a day, and will be continued for the next 3 weeks at that dose. At the end of each 12-week period, the drug (either baclofen or placebo) will be tapered over 6 days.

Children's carers will given information on possible side effects, and asked to contact one of the researchers if any adverse events occur.