It depends on the medication. There may be some interference with benzodiazepines (e.g. antiepileptic drugs (AEDs), antiseizure drugs), immunosuppressants, barbiturates and some opioid-based drugs. We do not know to what extent cannabis may interfere with antidepressants and anxiolytics, but it could possibly be used in conjunction with them to control chronic pain, as well as reduce the need for them for certain conditions. This is an area of ongoing research, and we will try to uncover as much as possible regarding negative drugs interactions. Cannabidiol (CBD) in particular seems to desensitize the liver enzyme cytochrome P450 (CY P450), which processes many drugs. Therefore, it is wise to be careful with dosing cannabis when using medications that are processed by CY P450.
One of the best things about medical marijuana/cannabis is that it seems not to interfere with many of the more benign, over-the-counter medications (e.g. aspirin, ibuprofen, acetaminophen), but this is difficult to say for sure due to the dearth of information and research on this matter.
If you are worried about any of your current medications being interfered with, please ask us. Feel free to show us your current medication list as well, as this can help.