Reserpine is a medication that is primarily used to reduce high blood pressure. It belongs to a class of drugs known as antihypertensives, which work by relaxing the blood vessels and reducing the force of the heart`s contractions. This helps to lower blood pressure and improve blood flow throughout the body.

It is important to note that reserpine is not used to increase blood pressure when it is low. In fact, it can have the opposite effect and may cause a decrease in blood pressure.

Additionally, reserpine is not used to alleviate pain or cure arthritis. It specifically targets high blood pressure and is not intended for the treatment of other conditions.

Therefore, the correct answer is option 1 - reserpine is used to reduce high blood pressure.