Bloodletting for therapeutic purposes is usually limited and does not lead to thickening of the blood. Bloodletting, or bloodletting therapy, is a type of acupuncture therapy in Chinese medicine. This technique is a treatment method that uses three-pronged needles, thick millimetre needles or small sharp knives to puncture or cut specific points or parts of the body, releasing a small amount of blood, which has the effect of reducing swelling and relieving pain, opening the orifices and draining heat, and activating the meridians and collaterals. When using this technique, it should be noted that patients with skin ulcers, bloodsickness and bleeding tendency should not use it. Under normal circumstances, bloodletting therapy does not usually cause blood viscosity. If you need to use bloodletting therapy, it is recommended to go to a regular hospital for consultation and treatment under the guidance of a professional physician, and not to operate on your own to avoid delaying the condition.