Substitution can be categorised as the choice to use one drug (legal or illicit) instead of another due to issues such as:
- perceived safety;
- level of addiction potential;
- effectiveness in relieving symptoms; and
- access and level of acceptance.
The substitution of one psychoactive substance for another with the goal of reducing negative outcomes can come under the banner of harm reduction. Studies have shown that medical cannabis patients have been engaging in substitution by using cannabis as an alternative to alcohol, prescription, and illicit drugs. [i]
Some studies have found that medical cannabis laws are associated with significantly lower state-level opioid overdose mortality rates [ii]. Overall there is a data hint of substitution for opiates. There is little conclusive consensus regarding the direction that effects have on alcohol, but experience in the United States should soon give more data on this[iii].
Taking all these factors into account there are potentially promising signs regarding the substitution effect that cannabis has on the use of some drugs, however the data is far from definitive. Worthy of note is a research report from the Ministry of Health showing the estimated personal harm by drug group. We are all increasingly aware of the damage that methamphetamine does to society[iv]. To put a dollar value on it this report states this harm at $184,200 per dependant user of Amphetamine-type stimulants annually. Therefore any anecdotal evidence that can suggest cannabis may reduce the harm caused by meth is worthwhile investigating further.
The evidence is insufficient to say definitively the effect that cannabis has on other drugs however early signs suggest it can reduce the intake especially of opiates.