What are the long term effects of quitting Symbicort suddenly?

If you stop abruptly (cold turkey) you will experience withdrawal symptoms for 3 weeks give or take depending on your organism.

You may experience the following:

weakness, weight loss, nausea, muscle pain, headache, tiredness, dizziness

Hope you are ok, I would suggest you speak with your prescriber and if possible try to avoid discontinuing suddenly/abruptly.