The NHS plea comes after the Welsh drugs testing service found two in every five sample liquids tested last year contained one or more synthetic cannabinoid receptor agonist (SCRA).
SCRAs are associated with serious health issues ranging from breathing difficulties to psychotic episodes.
All of the liquids were bought in the belief they were cannabis, CBD or THC e-liquids.
The Welsh Emerging Drugs and Identification of Novel Substances (WEDINOS) has tested more than 33,000 samples across the UK since publishing its first test results in 2013 – which was on an unknown white powder from Newport which hospitalised someone who used it.
It tested 196 vape liquid samples in 2023, of which 75 contained one or more SCRA.
‘Risk is high’
The testing service is also concerned at a “huge rise” in samples of counterfeit prescription drugs which have been contaminated by dangerous substances.
Last year, it received 90 samples containing potentially dangerous Nitazene drugs, of which nearly half were bought in the belief they were anti-anxiety drug Diazepam.
Opioids account for the highest number of illicit drug-related hospitalisations, it said, followed by cannabinoids such as spice.
WEDINOS receives samples from a variety of sources, including police forces, health authorities, prisons and members of the general public.
Professor Rick Lines, head of substance misuse at Public Health Wales, said: “The increased risk of overdose from high potency drugs shouldn’t be underestimated.
“We are concerned that people may not be getting what they think they are getting when they buy drugs online.
“Prescription drugs should only ever be obtained from a GP. The risk of fatal overdoses is high from some of the samples we receive, especially when substances are used by those who don’t realise the risks they pose or when they are using them in combination with other substances.”
The professor said WEDINOS was “crucial to the harm reduction response” across the UK and expressed his gratitude for those who submit the samples.