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: dofetilide, orlistat.Other medications can affect the removal of lamotrigine from your body, which may affect how lamotrigine works. Examples include hormonal birth control (such as pills, patches), estrogens, other medications to treat seizures (such as phenobarbital, primidone, valproic acid), rifampin, ritonavir, among others. Your doctor may need to adjust your dose of lamotrigine if you are on these medications.This medication may decrease the effectiveness of hormonal birth control products (such as pills, patch, ring). This effect can result in pregnancy. Ask your doctor or pharmacist for details. Discuss whether you should use additional reliable birth control methods while using this medication. Also tell your doctor if you have any new spotting or breakthrough bleeding, because these may be signs that your birth control is not working well.Tell your doctor or pharmacist if you are taking other products that cause drowsiness including alcohol, marijuana (cannabis), antihistamines (such as cetirizine, diphenhydramine), drugs for sleep or anxiety (such as alprazolam, diazepam, zolpidem), muscle relaxants, and opioid pain relievers (such as codeine).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.This medication may interfere with certain laboratory tests (including urine drug screening tests), possibly causing false test results. Make sure laboratory personnel and all your doctors know you use this drug.