Crack cocaine use has risen sharply in the Netherlands over the past decade, replacing heroin as the most commonly used drug among people with serious addiction problems, according to new research by the Trimbos Institute and the Mainline Foundation.

The study estimates that 27,900 people in the Netherlands currently use crack, compared with 13,300 who use opiates. While most opiate users (89%) also smoke crack, around 16,000 people use crack alone — and three-quarters of them have never regularly used opiates.

Researchers say this suggests the emergence of a new group of users, many of whom are not in contact with addiction services, despite having complex health and social problems.

The study found that only 31% of people who use crack but no opiates are registered in the national addiction database, compared with 61% of opiate users. Both figures are lower than a decade ago.

The researchers interviewed 520 people in eight cities — Amsterdam, Rotterdam, The Hague, Utrecht, Eindhoven, Haarlem, Groningen and Heerlen. Their average age was 50, with the youngest 19 and the oldest 79. Some 85% were male and 49% born in the Netherlands, 11.5% were born in an EU country and almost 40% elsewhere.

The researchers also found that 40% were homeless and around 75% said they experienced mental health problems, but only 16% were receiving psychological care.

The use of needles to inject drugs is out of favour but more than 60% said they share drug paraphernalia such as crack pipes, which increases the risk of infectious diseases including hepatitis and herpes.