Nearly 6,000 discarded needles have been collected from Welsh streets since 2015, figures obtained by the BBC show.
More than 2,100 requests were made to local councils leading to more than 5,900 needles being picked up.
But the total amount could be significantly higher because not all Welsh local authorities provided data.
A Cardiff priest who regularly finds discarded used syringes near a school said he knew of cases where children had picked them up and taken them home.
Newport-based drugs charity Kaleidoscope said the problem could worsen amid real-term cuts to services that advise users on syringe disposal.
However, the Welsh Government insisted it had not cut its annual substance misuse budget.
The BBC asked every local authority in the UK how many reports they had received about discarded needles, and about 300 responded.
In Wales, Neath Port Talbot had the most, with 391 between 2015 and 2017. It was closely followed by Wrexham, where they were 390 and Newport, where there were 376 reports.
Newport had the highest number, where 3,460 needles were collected in 2018 alone - more than half the Wales total of 5,833 since 2015. The council did not provide collection figures for any other year.
But seven of the 22 Welsh councils failed to respond to the Freedom of Information inquiry, including some of Wales's most populated areas such as Cardiff, Swansea and Rhondda Cynon Taff.
The total number of needles collected in Wales is likely to be higher because only nine Welsh councils supplied figures for this question.
Those which did not included Cardiff, Neath Port Talbot, Rhondda Cynon Taff and Wrexham.
Pembrokeshire council said it did not keep such data but said street cleaning teams got rid of syringes by using "sharps" disposal units and then handing them in to local chemists.
Father Dean Atkins, of St Mary's Church in Butetown, told BBC Radio Wales: "Across Butetown, residents find discarded needles on pavements, in gutters, on the steps of community halls near school and in my church car park just yards from where I live."
He said plastic casing provided with the needles to help ensure safe disposal are colourful, and therefore attract children's attention, adding he had heard of children taking them home.
Father Atkins believes Cardiff council should explore providing safe spaces, or "fix rooms" for people to inject drugs, to combat the problem. The council has been asked to comment.
Martin Blakebrough, chief executive of Kaleidoscope, said it worked with drug users to stop them from injecting on the street.
He said: "You give people a syringe and then there is a danger that you don't have the opportunity to provide them with the information on how to dispose of them."
The Welsh Government said it gives £22.6m a year towards tackling substance misuse, including needle and syringe programmes aiming to reduce the number of viruses and infections caused by sharing equipment, as well as reducing "drug-related litter".