Hypothetical situation- A person is taking 2 anabolic steroids (testosterone and nandrolone decanoate), and is prescribed a 6 day course of prednisone to treat swelling in the knee joint.
First, are there any dangerous interactions?
Second, are there any interactions which would increase, or decrease, the effectiveness of any of the drugs involved?
No.
No.
Got a cite?
No warnings about “tell your doctor” about anabolic steroids in the government’s description of prednisone via MedlinePlus or listed contraindications in a (PDF) manufacturer’s drug information sheet.
(by CP) No. No.
Me.
I don’t mind answering questions, but if you are looking for more than that (why? 
) there are plenty of educational sources online that can point you to the differences between one type of steroids and another.
I know the differences, I was just having trouble finding a source for their interactions. I imagine the water retention/weight gain which is normal for both prednisone and nandrolone would be even more pronounced?
Both nandrolone and prednisone have some mineralocorticoid activity, which is essentially additive if you take them at the same time. However in typical doses of prednisone, a 6 day course is not going to produce a dangerous interaction. Let’s pretend we’re talking about a guy who uses anabolic steroids on an ongoing basis, has gummed up his knee and now gets put on a short course of (typically) tapering glucocorticoids such as prednisone. His kidneys are already used to the baseline mineralocorticoid effect of the nandrolone. Now he gets put on prednisone. What will happen (or, for the very nervous, what might happen)?
What will happen is nothing. Six days; tapering doses; not typically higher than a starting dose of 30 mg prednisone/day. 60 mg max.
What might happen? Well, pretend for a moment that unbeknownst to the patient his potassium is already dangerously low. He hasn’t been getting enough potassium in his diet to replace the mineralocorticoid effect of the nandrolone and has severely depleted his intracellular stores. Now he adds prednisone, drops his K+ over the tipping point, has a vigorous workout (despite the bum knee), sweats and gets dehydrated, replenishes with plain water, dilutes his K+ even more, gets a fatal arrythmia from the low potassium and croaks. All from following crummy advice he got on the SDMB.
The odds of bumping yourself off from a low potassium (and that’s pretty much the only potentially dangerous interaction of anabolic steroids and glucocorticoids) are not zero, but in your scenario they are trivial. It may be the case that a physician might recommend bumping your potassium-containing foods if she knew about the nandrolone.
As to the weight gain question: any additional weight gain from the prednisone would be from its mineralocorticoid effect (with such a short length of therapy); you’d pee off the extra water and salt back to your baseline as soon as you stopped taking it. 6 days is not enough to get a redistribution of fat. Your main weight gain enemy is gonna be a bad knee and inactivity.
I hope this longer answer reassures you I was not being overly flippant with the first.
CP, MD, ABIM, ABEM
No, I never thought you were. I think other posters might have thought so.
Your first post was what I needed to see…then I realized I’ve gotten a little puffy in the face this week and I was wondering if the body had a “limit” of how much water you could retain, and the prednisone wouldn’t cause any additional swelling, or if there is a slight cumulative effect, which your last post answered.
Thanks
And the knee won’t keep me inactive, I’ll still be able to do spinning classes for aerobic workouts, I just can’t play basketball or football for awhile.