After many decades of prohibition, the US is undergoing a state-by-state liberalization of cannabis laws. Medical use of cannabis is now allowed in 23 states, and Colorado, Delaware, Washington (state), and Washington, DC, have all legalized the possession and recreational use of the drug.

While the medical establishment doesn't have a lot to say about the dose required for recreational activities, it does tend to care about medicinal uses. A new paper in JAMA this week suggests that in the majority of cases, the amount of psychoactive ingredients in the medical edibles is significantly less than claimed.

The authors identified cannabis dispensaries in Los Angeles, San Francisco, and Seattle that sold cannabis baked goods, drinks, or candy with packaging labels that identified the amount of tetrahydrocannabinol (THC)—one of the primary active compounds in cannabis. After selecting three in each city, they purchased a total of 75 different edibles (from 47 different brands) and took them back to the lab to determine the actual amounts of THC in each. They also looked for cannabidiol (CBD), another psychoactive compound that some products provided an amount for (others didn't).

Using high-performance liquid chromatography (which separates out compounds from a mixture using a solvent and a sorbent-filled column), they discovered that only 17 percent of edibles had as much THC as their labels indicated (within 10 percent). Another 23 percent were underlabeled, containing 10 percent more THC than claimed. But a massive 60 percent were overstating the amount of THC contained by at least 10 percent.

Edibles from Los Angeles were most likely to fall into this category, with Seattle's products the most likely to understate THC levels.

Things were worse when it came to CBD. Only 13 products listed CBD values, yet 44 contained detectable amounts. Of the 13 with information, nine overstated the amount of CBD present. And the CBD present was also problematic; studies have shown the greatest clinical benefit from cannabis products happens when those two compounds are in a 1:1 ratio. Only a single one of the tested products achieved this.

These findings aren't the first to find problems with the labeling of cannabis products, either. Last year, The Denver Post also found that many edibles were overlabeled.

This is obviously a problem for therapeutic users in California and other states where edible cannabis products are allowed for medical conditions. Those seeking relief from pain or taking doses for other medical uses ought to be assured that the levels of THC and CBD match what the packaging says, in the same way that they can be sure that a 200mg tablet of ibuprofen actually contains 200mg of ibuprofen. Recreational users may also be in for some unpleasant surprises if the active compounds differ so much from brand to brand.

The fragmented and quasi-legal status of cannabis across the US probably hasn't helped this situation. Getting into the weed business, even in CO or WA where it's been legalized by the state, isn't like setting up a new drug company or even a new candy company. The drug remains illegal at the federal level, and since US banks are regulated federally, cannabis businesses can find it impossible to get bank accounts. Many cannot accept debit or credit cards or checks.

At least one state may see the chaos brought under control. Cannabis is big business in Colorado—about $700 million big ($313 million of which was recreational) in 2014, of which 10 percent went back to the state as taxes and revenue. Earlier this year, the state enacted new regulations for the edible pot market, requiring makers to actually test the potency of their products (and to block them from sale if they aren't up to scratch). Cannabis cooks, you can all do better.

JAMA, 2015. DOI: 10.1001/jama.2015.6613 (About DOIs).