I just injected 40 units of lantus (insulin glargine). it bled a decent drop until i pressed the area with my boxers. how can you tell if you inject into a vein?

Don't Worry: This is an old concern & particularly with rapid insulin. With insulin pens & small needles it is hard to hit a large vein. You most likely hit a venule, a very small branch of a vein, & the needle will actually pass through it. The insulin will deposit behind the vein the Lantus (insulin glargine) slowly release, but you will bleed a little. If Lantus (insulin glargine) is in a venule it will likely clot & the Lantus (insulin glargine) work normally.