The number of prescriptions for Viagra and other erectile dysfunction drugs has nearly tripled in the last decade as they become cheaper and carry less stigma.

Figures from NHS Digital show there were 2,958,199 prescriptions for sildenafil in 2016, compared with 1,042,431 in 2006. Prescription numbers rose by 43% between 2014 and 2015, and by 16% between 2015 and 2016.

The Royal College of General Practitioners (RCGP) put the sharp rise down to growing awareness, the drug becoming cheaper and less stigma being attached to buying it, with more men feeling “comfortable enough to visit their doctor”.

But they also warned about the dangers of buying Viagra off-prescription online, as data showed £17m worth of unlicensed and counterfeit Viagra was seized last year.

Doctors have noted a trend of younger men buying the drug on the internet to improve sexual performance or to counter the use of other recreational drugs they have taken that make it harder to get an erection.

Prof Helen Stokes-Lampard, chair of the RCGP, said it was not a good idea to buy sildenafil citrate, the generic name for Viagra, off-prescription online. She said it was a “powerful drug that could have potentially unpleasant side-effects, and serious interactions with other medication”.

She said: “Buying medication online might seem convenient, and it might be attractive to patients who are embarrassed to discuss medical problems with their doctor in person, but it isn’t without risk. Firstly, there is no way for someone to know what they are buying is what they think it is, and this in itself can have profound consequences.

“There are a number of medical reasons why the drug would not be prescribed – for example, if a patient has a heart or liver problem, or if they have low blood pressure.”

The Medicines and Healthcare Products Regulatory Agency (MHRA) said more than £17m worth of unlicensed and counterfeit Viagra was seized last year, down from £20.9m in 2015-16 but well up on the 2014-15 figure of almost £7m.

A number of websites now sell generic products cheaply without prescription, but research has shown a large percentage of it could be fake.

The cost of Viagra fell by 85.9% as generic alternatives became available in 2013 and it became available for a wider range of conditions.

Danny Lee-Frost, head of enforcement at MHRA, said: “We see a lot of unlicensed generic erectile dysfunction medication coming out of India, it’s a big problem ... so this is pharmaceutical companies in India making their own versions of these medications. They are not licensed for supply in the UK, so they cannot be supplied by a UK doctor and end up on websites dotted around Britain.”

He added: “The other way it comes in is from someone based in the UK: the term for that is a drop shipper. They get big parcels from suppliers from the far east or China and that becomes their stock that they then distribute out in the post … we will seize big parcels heading on their way to drop shoppers and try to work out where the shipper is to arrest them.”

Seth Rankin, an NHS GP and chief executive of the London Doctors Clinic, a private chain of GP surgeries, said he had heard anecdotally about young men buying Viagra online. “We see a number of guys who take [Viagra] recreationally and we might get a sideways question like, ‘my mates are using it – is there any harm?’ You don’t get people coming in and asking for it directly, most get information from friends and order it online.”

He added: “It’s the same thing as steroid use in gyms, they are usually a bit worried about taking it and want to check it’s OK.”

Rankin said many millennials took the substance because they watched a lot of pornography and felt pressure to perform. But they also took it to counteract the effect of substances such as alcohol or drugs, which can cause erectile dysfunction.

Hayley Quinn, a dating expert, agreed that Viagra use was becoming more common. She said it was common for men to be more concerned about performance than women might think.

“The ease of purchase for Viagra has increased,” she said. “These people are using Viagra recreationally or to counterbalance other recreational drugs … it’s seen as boundary pushing, for a certain set of people. How they feel about Viagra has changed and it’s seen as something that enhances sexual performance.”