The government's drug advisory panel is meeting to decide if a decision to downgrade cannabis should be reversed after worries about mental health.
A cannabis cigarette being rolled
Home Secretary Charles Clarke has asked the panel to particularly look at high strength cannabis, known as "skunk".
When the Advisory Council on the Misuse of Drugs met in 2002, evidence stated cannabis could worsen some conditions.
Studies since have said the drug can cause psychiatric problems, while the Dutch may now outlaw stronger strains.
In the UK, the council's conclusions three years ago helped persuade the government to make cannabis a class C rather than class B drug.
Police officers were also told not to arrest adults for possessing the drug for their own use.
However, there are new concerns because skunk and other more-powerful varieties of cannabis contain high levels of Tetrahydrocannabinol (THC), the active ingredient.
In Holland the potency of cannabis has increased, leading the government there to consider reclassifying some strains alongside harder drugs.
One British father believes smoking cannabis helped precipitate schizophrenia in his son six years ago.
Terry Hammond, from Southampton, told the BBC his son Stephen, 27, started hearing voices after a "binge" on cannabis joints.
Mr Hammond believes cannabis triggered his son's mental illness
"He collapsed in a disco, and when he came round he heard voices saying 'it's OK Steve - you can get up' but there was no-one there talking.
"He has heard them ever since. The doctors are saying it [cannabis] was definitely a trigger."
Mr Hammond, who works with mental health charity Rethink, added: "The anecdotal evidence is screaming at us, there are not an insignificant number of people being affected by cannabis."
And Paul Smedley, of drug awareness charity Dare UK, said cannabis should not have been reclassified, calling the move to Class C "quite dangerous".
When Mr Clarke wrote to the Advisory Council on the Misuse of Drugs this March, he highlighted concerns over studies that strongly-linked cannabis use to the development of psychosis.
However, he also wrote that since the downgrading of cannabis there had been no proven increase in use of the drug.
Metropolitan Police chief Sir Ian Blair, the UK's top police officer, has also said he does not want the relaxation of cannabis laws reversed as dealing with small amounts of the drug wasted police time.
And Harry Shapiro, of Drugscope, also told the BBC: "We think the government made the right decision, particularly in terms of policing priorities about where the effort should be in relation to drugs.
"More officer hours are now being spent dealing with more serious situations like heroin and crack."