A legal cannabis user said he was "caught off guard" after unexpectedly receiving a letter asking him for proof of his medical condition.
Ryan Specter, of Wilson Place in Poringland, is a UK registered medicinal cannabis patient which he uses to help with his attention deficit hyperactivity disorder (ADHD).
The 27-year-old was sent a letter at the end of last week from the government Driver and Vehicle Licensing Agency (DVLA) enquiring into his fitness to drive.
Mr Specter was asked to submit completed forms with proof of his medical condition within 14 days or his provisional driving licence would be revoked.
The DVLA has said it will be contacting Mr Specter to apologise for the letter.
Mr Specter is prescribed Adven Flos19 by London-based private pharmacist provider Sapphire Medical Clinics.
The legal cannabis user said: "A cannabis naïve patient who may not be aware of this and is pulled over by police will not know how to handle that situation.
"They could end up in court or with a fine when they could have otherwise contested it by arguing their reason for using it."
A spokesman for the DVLA said the letter was sent by mistake.
Mr Specter added such errors are usually a rarity.
And he also emphasised the onus is on the driver not to get behind the wheel in situations where it will affect their ability to operate the vehicle safely.
It comes following an incident which saw his medication seized by police and then later returned to him.
Norfolk Police said they would not be commenting on a complaint to the Professional Standards Department until an outcome is reached.
Government law introduced in 2012 gives the police powers to test and arrest drivers suspected of driving after taking certain controlled drugs in excess of specified levels.
This law also provides a medical defence if a user is taking medicine in accordance with instructions from a healthcare professional.
Legal cannabis users are advised to keep evidence of their prescription medicine by the government in case they are stopped by police.
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