I'm not currently taking any pd medications (other than sizeable amounts of CoQ10). Tried azilect for 6 weeks last winter and ended up with many small but annoying headaches and also flashing lights perceived only at night on the right periphery of my visual field. Stopped the azilect. The headaches ceased, the light flashes have continued. So if the antihistamine is potentiating something, it's not traditional pd meds (pedmeds?).