You are recommended to take some medicine to prevent altitude sickness ahead of time instead of when arriving in Tibet, since it'll help you to enjoy your trip better. Here are some recommended medicines:
Rhodiola capsules combined with Gaoyuan'an capsules are a good anti-altitude solution. Generally, you can take about two boxes of Rhodiola capsules (each box can be used for half a month) with one or two boxes of Gaoyuan’an capsules (two to three days per box).
It is suggested to take thess medicine one week before entering Tibet. During your stay on the plateau, you can choose whether to continue taking it according to your own condition. Please stay alert to your physical condition all the time. Rest more and exercise less. If you feel unwell, you should go to the doctor immediately.
In addition, you can bring some other medicines you may need:
Liquid Glucose is a must, it can help you to ease headaches and sickness caused by altitude sickness. Drinking glucose can also help you with your energy. Medicines for stomachache, cold, infections, pain relief, car-sickness and band-aid, etc. are recommended too.