Certainly many interactions naturally occur and it is very reasonable to assume that interactions may potentially occur between marijuana and prescription medications. However, it is not reasonable to assume that the interaction between marijuana and every prescription medication will be in the same direction and of the same magnitude.
When present:
– interactions are positive or negative (meaning that you may need less or more of the medication in question to achieve the desired effect).
– interactions can be additive (linear), multiplicative or exponential.
– multiple interactions can simultaneously occur (which also have the potential of canceling each other’s effect)
– interactions (with marijuana) are not constant (with prescription medications), meaning that the interaction between marijuana and an antihypertensive medication will not be the same interaction between marijuana and an antibiotic or seizure medication (for instance).
– interactions may occur differently among individuals taking the same medications.
The long and short of it is that your physician and/or pharmacist can research the potential interaction, whether it is present, in which direction it occurs, and to what extent it may occur, and modify your prescription accordingly.