Substance use disorder (SUD) or addiction to drugs/alcohol is a devastating disease. Over 40,000 overdose deaths have happened in Canada since 2016, 1 in 5 Canadians will have a SUD, and 70% of those with SUD continue to relapse, showing that we urgently need new treatments. The Helping Addiction by Individualized Therapeutic Stimulation (HABITS) Study is exploring deep brain stimulation (DBS) for people who have failed to quit harmful substances. Over 250,000 people have received DBS, which is well-established for Parkinson's disease and has evidence of success in major depression and obsessive-compulsive disorder. DBS uses electricity to directly stimulate areas of the brain. However, for DBS to work effectively, it needs to be personalized to each individual, which will be pursued through stereoelectroencephalography (SEEG). DBS and SEEG are minimally invasive and reversible, with a low risk of side effects. SEEG started over 70 years ago to find seizure location in the brain of children and adults with epilepsy. It now has been used for major depression and chronic pain to guide DBS. It involves inserting electrodes temporarily across critical brain areas and monitoring patients for several days. SEEG can provide an understanding of where addiction and craving are in the brain to guide the placement of DBS electrodes and device settings that are optimal for a person. In the HABITS Study, 10 participants will receive DBS guided by SEEG and undergo 11 study visits. Individuals will first undergo detoxification with CAMH. Then, they will receive DBS and SEEG at Toronto Western Hospital, where they will stay for 1 to 2 weeks. Finally, they will be followed for a year, where they will receive standard psychiatric care. SUD causes heavy burdens on individuals, families, healthcare systems, and society. The HABITS Study promises to personalize DBS to treat those who are struggling with severe addiction.