If you have a hard lump in your arm after an injection, it may be formed by the accumulation of drugs, or it may be a local inflammatory change caused by drug stimulation. No matter which of the above reasons, you can generally solve the problem by the following treatment. 1, you can do some local hot compresses, hot towels with hot water bags or hot compresses with salt bags. Each compress for 20-30 minutes, twice a day, can promote local blood circulation, accelerate the dissipation of local hard nodes. 2, you can do some local physical therapy, such as ultrasonic therapy, infrared therapy or microwave therapy, can promote local blood circulation, accelerate the dissipation of hard nodes. Especially ultrasonic treatment can soften the scars or soften the hardened soft tissues so that the hard nodes can be softened and absorbed better.