Donald Trump has said that he is open to changing the law on cannabis after a previously undocumented side effect was discovered.

The US currently has a patchwork of different legal tolerances around the use of the drug, with precise rules varying by state. There are clear distinctions about whether the drug is being used recreationally or prescribed medically.

Cannabis can be prescribed for several uses such as chronic pain relief, where it is generally considered less risky than opioids, as well as in managing health conditions such as Multiple Sclerosis or relieve the side effects of chemotherapy.

However, legally there is a big difference in the US between medical use and recreational use, and for recreational use, it varies a lot by state, with some legalizing possession of a relatively small amount, though many also have laws around where it can be consumed.

Now, Trump has indicated that he wants to revisit the law around cannabis in the US, though he made one admission about the issue. At a press conference earlier this year, the POTUS suggested that his administration may revisit the classification of cannabis.

He said: “We’re looking at reclassification, and we’ll make a determination over the next – I would say, over the next few weeks, and that determination hopefully will be the right one.”

In a remark which is perhaps surprising for a president known for his sweeping statements, Trump said: “It’s a very complicated subject.”

He added: “I’ve heard great things having to do with medical and bad things having to do with just about everything else.”

Cannabis is illegal on in the US on the federal level as a Schedule I under the Controlled Substances Act of 1970. However, states have been able to introduce ‘exemptions’ to this for certain circumstances.

Many jurisdictions have a medical exemption, for example, but others such as California have gone further with exemptions for possessing smaller amounts for personal recreational use.

Trump’s comments have re-emerged after previously unknown side-effects for regular and long-term users of cannabis were identified by scientists.

This has been called cannabis hyperemesis syndrome (CHS), and can trigger symptoms like nausea.

Emergency medicine specialist, Dr. Chris Buresh, said: “Some people say they’ve used cannabis without a problem for decades. Or they smoke pot because they think it treats their nausea.

“It seems like there’s a threshold when people can become vulnerable to this condition, and that threshold is different for everyone. Even using in small amounts can make these people start throwing up.”