Innocuously marketed as incense or bath salts, synthetic drugs are increasingly popular among Portuguese youths looking for a legal high, despite a ban on selling them to minors.
Adverts for these substances, responsible for a growing number of hospitalisations, are plastered around Lisbon and have now caught the eye of health authorities who have decided to wage war against the dozens of so-called smartshops selling them.
The proliferation of these synthetic drugs, which reproduce the effects of illicit drugs like cannabis, cocaine or ecstasy, and of hallucinogenic plants, has already created problems for other European legislators, and Portugal is the latest to launch a crackdown.
The country introduced legislation in 2001 that decriminalised drugs use across the board, a move that health experts credit in part for the decline in drug addiction. Users are now forced to appear in front of special addiction panels rather than a criminal court.
Now, legislators are turning their attention towards synthetic drugs, with officials on the popular tourist archipelago of Madeira the first to have raised concerns over their use in the country.
"Local authorities sounded the alarm because the consumption of these psychoactive substances has increased dramatically in a short amount of time, with serious consequences to boot," national health director Alvaro Carvalho told AFP.
Since January 2012, four people have died and 170 others have needed hospital treatment for psychotic episodes and cardiac complications, he added.
This month, the regional government enacted a law banning the sale of any psychoactive substances listed by the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA), leading to the closure of the island's smartshops.
National legislators plan to also submit a bill on the subject in the coming weeks in a bid to curb consumption, taking their lead from measures put forward by other European countries such as Britain and Italy.
Compounding the problem, however, is the fact that the goal posts keep moving: synthetic drug makers regularly switch the chemical make-up of their products as each new substance is outlawed.
The EMCDDA has detected 57 new substances since the beginning of the year alone.
In Lisbon, a dozen smartshops are scattered around the bars and clubs of the trendy Bairro Alto and Cais de Sodre districts, with water pipes and rolling papers on display.
Interspersed among these items are the legal drugs: small packets of eye-catching and colourful design that promise exciting evenings at competitive rates starting at around 10 euros each ($13).
"Our customers are above all looking for legal alternatives they can get without running the risk of getting attacked or arrested," said one smartshop owner, who wished to remain anonymous.
But according to Joao Goulao, chairman of the EMCDDA, "the over-the-counter availability of these substances gives a false sense of security, which is really not the case".
A growing number of hospitalisations -- often of users in a critical condition -- has been seen and medical personnel struggle to respond "due to their lack of knowledge of the substances", added Goulao, who was among the architects of Portugal's decriminalisation law.
For Marco, a regular cannabis user in his thirties who first bought from a smartshop two years ago when he found it harder to buy from his usual sources, the effect of synthetic marijuana is "much stronger" than that of the illicit kind.
"I've experienced three episodes of a drop in blood pressure in six months, while that only happened once in several years of doing real cannabis," he said.
Given the official crackdown on the substances and increased media coverage of their consequences, some smartshop owners are planning their next move.
"Once the products are banned, we will respect the law and adapt," said one owner who wished to remain anonymous and kept his post-ban plans secret.
Marco, for his part, voiced concern over the potential repercussions of such a law.
"Those who experimented with these drugs when they were legal, what will they do now? Move on to illicit drugs?"