I'd like to recommend you Chinese traditional medicine---Cooling essential balm. It's made up of mint, camphor and other plants. Totally natural medicine, maybe not suitable to call it a medicine. It is a very normal home care product in China. Beside prevent mosquito bites, it can also relive the headache caused by heat stroke, cold, or carsick.
By the way, it is only 3g or 10g per iron box, easy to take, and can be a nice gift. One important point, it is quite cheap if you buy directly from me. Because I will buy them directly from factory in China.