Illinois allows certain deductions to Illinois-registered medical marijuana cultivation facilities. The form used is Illinois Form MC-3. Here's a link to that form: http://www.revenue.state.il.us/taxforms/Misc/MedicalCannabis/MC-3.pdf
Here are the form's instructions: http://www.revenue.state.il.us/taxforms/Misc/MedicalCannabis/MC-3-Instr.pdf
An individual taxpayer cannot take a tax deduction for the cost of medical marijuana.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
