Myasthenia gravis is caused by your immune system attacking the nerves that tell your muscles to contract. It is treated in two main ways. First, a drug can be given to slow down your immune system using an immunosuppressant like steroids. Alternatively, a drug can be given to turn up the signal that tells your muscles to contract. The signal for contracting is a chemical your body makes called acetylcholine. We turn up this signal by blocking acetylcholine breakdown - these drugs are called acetylcholinesterase inhibitors.