Hypertension is no less common in mainland China than it is in our respective Western countries. Consequently, you won’t have any difficulty finding all the classifications of medications used back home in China for the treatment of hypertension.
In smaller cities (second and third tier), you may have trouble finding a specific medication within a particular classification but can (almost always) find a substitute within the same classification. For example, if your doctor has you taking Avapro (Irbesartan, a commonly prescribed ARB, Angiotensin II Receptor Blocker), you may have trouble finding that in a given second-tier city but will have no trouble finding Diovan (Valsartan, another commonly prescribed ARB)… or vice versa. Generally speaking, there are no negative consequences to switching to a different hypertensive medication within the same classification of drugs.
One way or the other, you will be able to successfully treat your hypertension in China. Concerns over the availability of anti-hypertensive medications should not dissuade you from teaching English in China.