If you are taking lamotrigine how long does it take to get out of your system?

Lamotrigine will be out of your system after your last dose in about 338.8 hours (approximately 14 days).
After multiple dosing (in volunteers who took no other medicines) of lamotrigine the elimination half-life is noted to be between 11.6 to 61.6 hours.
It takes approximately 5.5 x elimination half-life for a medicine to be cleared from your body which for lamotrigine would take 5.5 x half life (5.5 x 61.6 hours (max))  338.8 hours. 

However other factors to consider include:
1. How much and how often you have taken the drug.
2. Your metabolic rate – a slower metabolism will increase the time a drug remains in your system.
3. Your age and health – older age and poor health will generally increase the time the drug stays in your system.
4. Body mass – generally the bigger you are the longer a drug will remain in your system.

https://www.drugs.com/pro/lamotrigine.html