If i have a gai of 91 in the 27th percentile will my drug use such as cigarettes and medical marjuana bring me to a less than 91 score to below average intellectual functioning ?

Your question is not intelligible. What is GAI and what does it have to with intelligence? For healthy diet: http://www.choosemyplate.gov/., exercise 30 minutes/day, drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs.

Yes. Cannabis use has been shown to impair cognitive functions on a number of levels—from basic motor coordination to more complex executive function tasks, such as the ability to plan, organize, solve problems, make decisions, remember, and control emotions and behavior. An Evidence Based Review of Acute and Long-Term Effects of ...https://www.ncbi.nlm.nih.gov › articles › PMC3037578