Hi
Any medicine will have side effects as they are chemicals. We need to way the beneficial effects & side effects & decide what is good for patient. As for Olimelt, drowsiness & weight gain are main side effects apart from few others. Just because its 10mg doesn't make it very high dose if that is the requirement of a patient.
How is your sister doing after the treatment has been started? If there is an improvement, don't worry so much about side effects.
However your sister needs to be evaluated to confirm the diagnosis. In case of OCD some medicines need to be added.
Next Steps
Discuss with treating doctor.
Health Tips
Always discuss about medicines with your doctor never take any decision on your own.