Acute Mountain Sickness (AMS) can affect anybody at an altitude of 2500m or more. It does not depend on whether you are fit or have been at high altitudes before. Anyone is susceptible and we take the risks seriously when on tour. On our Upper Mustang tour, we ride up to 4000m and 5000m accordingly. We must therefore be careful of the risks. We have staged our tours to minimize the possibility of AMS and have not experienced any serious issues to date. We carry Diamox with us but we recommend bringing your own supply. Diamox is a preventative medication rather than a treatment and must be taken several days before riding into altitude. It is also important to keep hydrated when at altitude and drink up to 5L of water per day. The symptoms of AMS are dizziness, nausea, headaches, and disrupted sleep. Vomiting is an indication of advanced AMS and requires immediate action which involves moving to a lower altitude.