How long does it take for Diastat to work? What are common side effects of Diastat? Is any special monitoring needed when Diastat is given? Oral Rescue Medicines 101. What are lorazepam and diazepam used for?. How long does it take for Lamotrigine to work? It is very important to tell your doctor how you feel things are going during the first few weeks after you start taking lamotrigine. It will probably take several weeks to see big enough changes in your symptoms to decide if lamotrigine is the right medication for you. Lamotrigine and Sodium Channels. As Medline explains, lamotrigine is an anticonvulsant medication, which means that it works to prevent abnormal electrical activity in the brain. I'm in the process of titrating my lamictal dose up from 25mg to 100mg. I was at 50mg for 2 wks and and this week going up to 75mg. I have not felt well at all so far, just very depressed. Approval And Uses of Lamotrigine. In the United States, this drug received marketing approval way back in December 1994 and it was only in 2003 that it received FDA approval because of the benefits derived from it when used on bipolar patients. For many people the higher dose does not work for them and can cause side effects. You may talk to your doc about lowering the dose. I am on the some of the same meds you are on but I take nortriptyline the sister med of amitriptyline. I am not bi-polar but have the same chronic depression, anxiety and PTSD. How long will I need to take it for? Lamotrigine can be used both to prevent and treat the symptoms of bipolar disorder, so how long you are on it will depend on the reasons you are using it. Lamictal does take time to build up in the patient's system and it may take some time before you start feeling the full benefits of the medication.