Please note that Hawaii law only allows medical marijuana. There is currently no special marijuana tax as a proposed 25% tax was removed in the final version of the law. As such the only tax that will be applied to medical cannabis is the standard General Excise Tax which is between 4 and 4.5%.
The state of Hawaii does not currently have a tax on marijuana, but there is talk of loopholes on tax breaks for dispensaries. There has been research done on the possible tax revenue for states, as observed from sales per capita from states like Colorado and Washington, where there is a tax on recreational and medicinal marijuana. In Hawaii, if there were to be a 15% tax, the revenue could range from $24 to $39 if there is a 25% tax.