IV drug users

how come there window period is 6 months ?

[Teak]

That question has been answered over and over again. You can find the answer in the achieves.

[Frank303]

Most don't exactly look after themselves well.

[wee540]

iv drugs tend to affect the immune system supposedly, decreasing activity

[Frank303]

Heroin slows everything down including the immune system. Also there is a higher risk of an IV user actually having HIV due to needle sharing (despite needle exchange progarmmes). Their last risk date is usually not known.
Though I don't know if it is injected, inhaled or sniffed methamphetamine users are as high risk of contracting HIV.