I'm sure its a common experience of needle programme workers around the UK (even around the world), people asking for 2ml barrels when they are planning to groin inject. But a 2ml isn't the best equipment for this and it's a behaviour that we as workers or peer educators need to challenge.
Why do people ask for 2ml
In the geographical area I worked in the main reason was one of historical availability, and I think this is the case in many areas. Often it's because pharmacy exchanges, and even some main site needle & syringe programmes (NSPs) didn't stock 1ml barrels as standard. The county I worked in used to use a ready made series of 'exchange packs' in both the NSPs and the pharmacies, the only pack available with needles long enough for groin injectors was the "2ml steroid" pack.
So with this historic availability it's not really a surprise that a culture develops where a 2ml barrel is seen as the kit of choice for the groin. As a result I now often find people who say it just doesn't 'feel right' injecting the groin with any other size of barrel.
There is of course another reason people ask for a 2ml, and that's because no one talks to them about the alternatives.
Why a 1ml is better
It's a simple matter of volume. A 1ml barrel can contain a volume of just over 1ml of fluid (the clue is in the name) but a 2ml barrel contains over 2.5ml of fluid. This isn't in itself an issue for injecting into the groin, after all the femoral vein is relatively large and can cope well. But many injectors continue to 'flush' after the injecting process is over. Flushing is the repeated drawing back of blood into the barrel and back into the vein, in the perception that this will help deliver more of the drug. (I've written about flushing before).
When using a 2ml though this flushing involves far greater volumes of blood, and as a result increases the risk of damage this this major vein.
So the next time someone comes into the NSP you work in, or your friend who goes in the groin asks you get get them kit, encourage them to go for a 1ml barrel not the 2ml.
Low dead space
Any separate needle/barrel combination introduces the risks of 'high dead space' from a blood borne virus (BBV) aspect this is a risk (previous article on this). It's this 'dead space' that gives injectors the perception that they are losing some drug if they don't flush (although in reality this is a minimal amount, especially in a 1ml barrel). Now though Exchange Supplies have started stocking low dead space 1ml barrels, the main reason is of course to minimise BBV risks, but the added benefit of delivering a greater amount of the drug is a major point for us to target injectors with. These new barrels also come in the now iconic multiple colours to help discourage accidental sharing.