"Caring for a patient who's taken an unknown legal high is the medical and toxicology equivalent of winging it," says Dr David Caldicott, who works as an emergency doctor at Nevill Hall hospital in Wales and specialises in illicit drug use. Even though Dr Caldicott is a specialist, he admits treating patients who have taken an unknown substance is tricky.

Why doesn't my doctor know about legal highs?

Legal highs are often brand new and untested on humans. So, medical types don't have the knowledge and experience that they have with well-known illegal drugs such as heroin or ecstasy.

"We can make an educated guess," Dr Caldicott says. "But, from our perspective, it's a whole different kettle of fish.

"Heroin is a very dangerous drug and potentially lethal, but every emergency medic knows how to deal with it. With legal highs, we have no idea what you're on. So while there may be a decreased hazard in strength, there's an increased hazard due to lack of familiarity."

What's more, these drugs keep changing. The chemical make-up of synthetic legal highs is in constant flux to keep on the right side of the law, so medical experts are always playing catch up. Dr Caldicott says it takes months to even get an idea of the effect of a new drug. Doctors can try and work out what type of drug you've taken (is it a stimulant or a downer?) and treat you according to your symptoms. But there's no way of knowing exactly what to do when they have no idea what you're on.

What are the health implications of taking legal highs?

How long is a line of cocaine? These synthetic substances are so new, and so untested, that it's impossible to say exactly what the health implications are. But there are some common patterns.

"It's the impact these chemicals have on people's psychological health that I find worrying," says Dr Caldicott. "I've seen lots of people who have tried to kill themselves while on legal highs. They change your mood so you don't see sense anymore. Quite often we need to restrain patients."

Other potential concerns are changes in blood pressure and problems breathing.

How can I protect my health when I'm taking legal highs?

Dr Caldicott says that if you are going to take legal highs, you should follow this advice:

• Don't mix your drugs - especially with alcohol.
• Ideally don't use a drug you haven't tried before.
• Don't take legal highs if you have mental illness.
• If you take a legal high and you end up in hospital, try and bring a sample of what you've taken to give to medical staff.

Photo posed by model

Updated: 28/03/2012

Holly Thompson