Hi, Trileptal (oxcarbazepine) is an anticonvulsant or antiepileptic medicine. It is used either alone or with other medicines(like your zonisamide) to treat partial seizures. Lyrica (pregabalin) is an anti-epileptic drug, also called an anticonvulsant. It works by slowing down impulses in the brain that cause seizures. The most common side effects of Lyrica are an infection, blurred vision, constipation, confusion, neuropathy diplopia, dizziness, drowsiness, fatigue, headache, peripheral oedema, tremor, weight gain. You should know that using (Trileptal) together with pregabalin may increase side effects such as dizziness, drowsiness, confusion, and difficulty concentrating. Some people, especially the elderly, may also experience impairment in thinking, judgment, and motor coordination. For this reason, I suggest to consult your treating neurologist and discuss with him the risks and benefits of the combination of Trileptal and Lyrica and then to decide what is the most appropriate treatment for you. Hope I have answered your query. Let me know if I can assist you further.