Don't worry it will not create more mucus, only make what's already there thinner in consistency and easier to shift.
Acetylcysteine is not a chemical drug by the way, but a form of the amino acid cysteine which has been modified to be more bioavailable. It is also a powerful antioxidant with many health benefits.
You might try 'Huff Coughing' . . . cftoo.blogspot.co.uk/2009/0...
"1. To prepare the lungs and airways for the huff coughing technique, you must first expel all the stale air in your lungs and airways. Begin by slowing down your breathing. Take slow gentle breaths, ending with one slow exhalation lasting three to four seconds.
2. Inhale slowly using your diaphragm. This is called diaphragmatic breathing or "breathing with your belly". This inhalation should be a slow comfortable breath; do not overinflate your lungs.
3. After inhaling a breath slowly, hold it for 3 seconds. This is done to control your breathing and prepare for an effective huff cough.
4. Tilt your chin up slightly and use your stomach muscles to make a series of three rapid exhalations with the airway open, making a "ha, ha, ha" sound. This helps to open the epiglottis in your throat and better allow the expulsion of the mucus in your airways.
5. Gain control of your breathing again by taking a couple slow breaths.
6. Repeat the huff coughing technique until the mucus has reached the back of your throat."