"Can cannabis help me regain my focus and be able to function while under the influence for my ADHD"
Most of the research so far relates to the concept of self-medication in people diagnosed with ADHD, including cannabis and various other substances.
While I am not aware of any specific medical evidence that cannabis use improves ADHD, judicious use of cannabis may improve study habits and grades. Clinically, I have had patients tell me that sativa strains during the day improve their focus.
Prescribed stimulants have side effects, including insomnia and indica strains of cannabis can be helpful for sleep. Improved sleep can improve anxiety and your ability to focus. Cannabis use may also decrease hyperactivity and impulsivity behaviors but there are no good studies documenting this that I know of.