More criminals in Northern Ireland are using social media and the dark web to sell drugs, according to a senior police officer.
Det Supt Rachel Shields said officers had also adapted their tactics to combat the online sale of illegal drugs.
The Police Service of Northern Ireland (PSNI) reported a 15% increase in drug-related arrests during the last year.
Cannabis was the most commonly seized drug, followed by benzodiazepines.
Det Supt Shields said she was particularly concerned about the online sale of illicit prescription medication.
"When we talk about illicit prescription drugs, it means they weren't prescribed to you by a doctor," she said.
"When you purchase such drugs online it's extremely dangerous because a doctor will have looked at your medical history and when you don't have that, you're running the risk of causing your body harm and in some cases it can be fatal."
She added that the drugs were often counterfeit and "could be a mixture of anything at any strength".
The majority of drug deaths in Northern Ireland are due to the misuse of a variety of prescription medicines.
According to the PSNI, there are about 100 organised crime gangs in Northern Ireland, with around a quarter believed to have connections to paramilitary groups.
Det Supt Shields says around 80% of organised crime in Northern Ireland relates to drugs and that criminals were increasingly using the internet to make money.
"They use various online platforms, there is the dark web and even social media and very often adverts that pop-up and people think it is a legitimate site, but it is actually criminals and organised crime gangs trying to advertise their business."
Det Supt Shields said the PSNI monitor social platforms for illegal activity and have a number of specially-trained detectives in this area.
She added: "Drug dealers might think they're more likely to get caught if you're out on the street, that online there is a level of anonymity.
"But the message from me is that you're not, because we adapt our tactics to try and catch these individuals."
The latest PSNI figures show that between April 2019 and March 2020 there were 3,819 drug-related arrests, an increase of 15% compared with the previous 12 months.
Figures also show that during the first five weeks of coronavirus lockdown measures being introduced, drug offences fell by nearly half in Northern Ireland, compared to the same period last year.
1 April 2019 to 31 March 2020
8,177drug seizure incidents
15% increasein drug-related arrests, when compared to previous 12 months
Det Supt Shields acknowledged that lockdown did have an impact on police operations.
"There is no doubt that we have been affected by Covid-19 and while possession offences and arrests may have reduced, this is temporary.
"We haven't taken our eye off the ball in relation to drugs and we have still had a number of successful operations in recent weeks."
At the end of April 2020, prescriptions drugs with a street value of £100,000 were seized. The counterfeit diazepam haul was part of an Organised Crime Task Force operation.
Det Supt Shields said: "These gangs are continuing to try and bring drugs into the country and cause significant harm within our communities.
"With drugs come guns, with guns comes intimidation and harassment and, meanwhile, individuals continue to line their pockets.
"They don't care about the consequences and then it's a vicious cycle."