New psychoactive substances (NPS) are a heterogeneous group of substances. They are associated with a number of health and social harms on an individual and societal level. NPS toxicity and dependence syndromes are recognised in primary care, emergency departments, psychiatric inpatient and community care settings. One pragmatic classification system is to divide NPS into one of four groups: synthetic stimulants, synthetic cannabinoids, synthetic hallucinogens and synthetic depressants (which include synthetic opioids and benzodiazepines). We review these four classes of NPS, including their chemical structures, mechanism of action, modes of use, intended intoxicant effects, and their associated physical and mental health harms. The current challenges faced by laboratory testing for NPS are also explored, in the context of the diverse range of NPS currently available, rate of production and emergence of new substances, the different formulations, and methods of acquisition and distribution.

Novel psychoactive substance (NPS) availability is increasing at a phenomenal rate and so is their associated misuse. Currently, the harms associated with NPS misuse are unclear. This report presents the initial findings of a continuing study looking into the impact of NPS misuse on admissions to an acute mental health facility in London. Violence preadmission and violence during admission have been found to be significant in NPS misusers compared to non-NPS substance misusers. Our findings have important consequences for acute mental health, emergency, and public health services. NPS misusers require specific assessment and risk management to reduce the risk of violence towards others.

Heval Özgen, Renske Spijkerman, Wim van den Brink and Vincent Hendriks contributed equally to this paper.

The term ‘opioids’ refers to both the natural compounds (‘opiates’) which are extracted from the opium poppy plant ( Papaver somniferum) and their semi-synthetic and synthetic derivatives. They all possess relatively similar biochemical profiles and interact with the opioid receptors within the human body to produce a wide range of physiological effects. They have historically been used for medicinal purposes, their analgesic and sedative effects, and in the management of chronic and severe pain. They have also been used for non-medicinal and recreational purposes to produce feelings of relaxation, euphoria and well-being. Over the last decade, the emergence of an illegal market in new synthetic opioids has become a major global public health issue, associated with a substantial increase in unintentional overdoses and drug-related deaths. Synthetic opioids include fentanyl, its analogues and emerging non-fentanyl opioids. Their popularity relates to changes in criminal markets, pricing, potency, availability compared to classic opioids, ease of transport and use, rapid effect and lack of detection by conventional testing technologies. This article expands on our previous review on new psychoactive substances. We now provide a more in-depth review on synthetic opioids and explore the current challenges faced by people who use drugs, healthcare professionals, and global public health systems.