See also Warning section.

Drug interactions may change how your medications work or increase your risk for serious side effects. This document does not contain all possible drug interactions. Keep a list of all the products you use (including prescription/nonprescription drugs and herbal products) and share it with your doctor and pharmacist. Do not start, stop, or change the dosage of any medicines without your doctor's approval.

Some products that may interact with this drug include: certain pain medications (mixed opioid agonist-antagonists such as butorphanol, nalbuphine, pentazocine), naltrexone, samidorphan.

The risk of serious side effects (such as slow/shallow breathing, severe drowsiness/dizziness) may be increased if this medication is taken with other products that may also cause drowsiness or breathing problems. Tell your doctor or pharmacist if you are taking other products such as other opioid pain or cough relievers (such as codeine, hydromorphone), alcohol, marijuana (cannabis), drugs for sleep or anxiety (such as alprazolam, lorazepam, zolpidem), muscle relaxants (such as carisoprodol, cyclobenzaprine), or antihistamines (such as cetirizine, diphenhydramine).

Check the labels on all your medicines (such as allergy or cough-and-cold products) because they may contain ingredients that cause drowsiness. Ask your pharmacist about using those products safely.

Guaifenesin is available in both prescription and nonprescription products. Check the labels of all your medications to make sure you are not taking more than one product containing guaifenesin.

Other medications can affect the removal of guaifenesin/hydrocodone from your body, which may affect how guaifenesin/hydrocodone works. Examples include azole antifungals (such as ketoconazole), macrolide antibiotics (such as erythromycin), mifepristone, HIV medications (such as tipranavir), rifamycins (such as rifabutin, rifampin), ritonavir, certain drugs used to treat seizures (such as carbamazepine, phenytoin), among others.

This medication may interfere with certain lab tests (such as amylase/lipase levels, urine levels of certain acids), possibly causing false test results. Make sure lab personnel and all your doctors know you use this drug.