Does the asthma medication "symbicort" (budesonide/formoterol) prevent or relieve the symptoms of asthma?

It does both: Budesonide (bud), a corticosteroid, treats the underlying inflammatory component of asthma - this makes the lungs susceptible to wheezing. Formoterol (fm) prevents exercise-triggered symptoms & relieves wheezing. It also reduces the need for higher doses of bud. Bud helps prevent the body from becoming unresponsive to daily use of fm. They work together symbiotically. Advair & Dulera (formoterol and mometasone) are similar.

Prevent: Symbicort (budesonide and formoterol) is a "controller" medication for asthma - it reduces asthmatic inflammation in the lungs, thereby preventing bronchospasm and its associated symptoms. Symbicort (budesonide and formoterol) is not approved in the United States for relieving the symptoms of asthma. Albuterol is the drug of choice to treat an asthma attack.

It should : Symbicort is a common medication for asthma. It should work well to relieve your symptoms. If not, talk to your pulmonologist about switching or adding different meds.