This medication has a risk for abuse and addiction, which can lead to overdose and death. This medication may also cause severe, possibly fatal, breathing problems. To lower your risk, your doctor should have you take the smallest dose that works, and take it for the shortest possible time. The risk for severe breathing problems is higher when you start this medication, or if you take the wrong dose or take more of this medication than prescribed. Taking this medication with alcohol or other drugs that can cause drowsiness or breathing problems may cause very serious side effects, including death. Also, other medications can affect the removal of this product from your body, which may affect how it works. Be sure you know how to take this product and what other drugs you should avoid taking with it. Get medical help right away if any of these very serious side effects occur: slow/shallow breathing, unusual lightheadedness, severe drowsiness/dizziness, difficulty waking up. Keep this medicine in a safe place to prevent theft, misuse, or abuse. If someone accidentally swallows this drug, get medical help right away. Before using this medication, women of childbearing age should talk with their doctor(s) about the risks and benefits. Tell your doctor if you are pregnant or think you may be pregnant. During pregnancy, this medication is not recommended. It may slightly increase the risk of birth defects if used during the first two months of pregnancy. Also, using it for a long time or in high doses near the expected delivery date may harm the unborn baby. To lessen the risk, take the smallest effective dose for the shortest possible time. Babies born to mothers who use this drug for a long time may develop severe (possibly fatal) withdrawal symptoms. Tell the doctor right away if you notice any symptoms in your newborn baby such as crying that doesn't stop, slow/shallow breathing, irritability, shaking, vomiting, diarrhea, poor feeding, or difficulty gaining weight.
Some products that may interact with this drug include: cimetidine, naltrexone, samidorphan. Guaifenesin is available in both prescription and nonprescription products. Check the labels on all your medications carefully to make sure you are not taking more than one product that contains guaifenesin. 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 morphine, hydrocodone), 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. Other medications can affect the removal of guaifenesin/codeine from your body, which may affect how guaifenesin/codeine works. Examples include azole antifungals (such as ketoconazole), bupropion, fluoxetine, macrolide antibiotics (such as erythromycin), paroxetine, quinidine, 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 urine 5-HIAA levels, urine VMA levels, amylase/lipase levels), possibly causing false test results. Make sure lab personnel and all your doctors know you use this drug.