Something that worked for me was I actually micro dosed deca. I only took 75mg a week and I didn't have side effects except for the stronger muscle I was building.

Anxiety is a common side for nandrolone for some people. The name of this game is finding compounds that agree with you. Not running those that don’t once you figure that out. You could try NPP. If it causes the same problem atleast it’s out of your system much quicker. Or just ditch nandrolone all together. It’s one of the most damaging drugs for your heart. You don’t need it to grow, there’s safer options that you might get on with better. Or stick to just test. If your current stats in your profile are accurate you tons more room to grow with just test. I hate saying “just test” as it makes it seem like an inferior and weaker option and it’s not. It’s a very powerful muscle builder. Building muscle is more about food and less about gear. You need some steroids to increase retention and protein synthesis and improve recovery, and a lot of food to support growth. 500mg of test with a great diet, training and sleep will take you a long way.

Deca gave me bad anxiety too. Wife cheating paranoia. Lowered the dose to half my test, I still had that anxiety but definitely lowered. Npp oddly enough doesn't give me that anxiety at all. Both fuck with my sleep if I take too much too though.

So I didn't do well my firs tgo around either. Damn mailman kept trying to bang my wife. But I tried again with NPP and I started at a lower dose and titrated up slowly. I also know how I felt the first time around so I could kind of feel those issue creep in again. But it worked out much better for me. Maybe don't jump in head first at 300mg

It’s worth a shot. For years, I thought I could not run tren because I had only tried ace and it makes me feel like shit. Also my temper flares up really bad and I’m constantly walking around with a chip on my shoulder.

A few years ago, I got crazy and tried Tren hex and later Tren E. I do not get any of the horrific tren sides with the long esters. They are some of my favorite compounds to run. I’ve tried Ace again and even at a very moderate dosage of 25 mg/day it fucks with my mind and body.

Food for thought, the Ester on Deca Is so long did it takes an absolute minimum of four weeks to stabilize. If you were feeling those sides after 10 days in very well, may have been something other than the Deca.

NPP and Deca are both nandrolones, but they don’t necessarily hit the same way for everyone. The ester length plays a big role here. Deca (long ester) tends to accumulate more in the system, leading to higher and more stable plasma levels, which can increase the risk of side effects like anxiety, lethargy, and mood swings for some people. NPP (short ester), on the other hand, peaks and clears faster, so in theory, if you react badly, you’ll notice it sooner and it’ll be out of your system quicker.

But here’s the thing … nandrolone itself has a high affinity for the progesterone receptor and also increases neurosteroids like allopregnanolone, which can mess with GABA regulation in the brain. For people who are already prone to anxiety or depression, that often leads to even more psychological instability. That’s why a lot of guys with your profile don’t tolerate Deca or NPP well, no matter the ester.

If you already had bad anxiety on 300mg Deca, there’s a decent chance NPP could trigger something similar. Some guys are fine, but for many, nandrolone + pre-existing anxiety = trouble.

Instead, you might want to look at compounds that are more “neutral” or even mood-enhancing:
DHT derivatives (Masteron, Proviron, Primo) … These usually improve dopamine activity and have a mild stimulating effect on CNS. They often make guys feel sharper, more confident, and more stable mentally.
Primo in particular pairs very well with test. It’s a slower, “cleaner” builder — less water retention, fewer estrogen/progesterone interactions, and way less likelihood of messing with your head.
If you want to push growth harder, you could stack test + Primo + a short oral (like Turinabol or Anavar). That’ll give you a solid anabolic environment without introducing something that might trigger anxiety again.

At the end of the day, this lifestyle is about feeling good while improving. If a compound keeps putting you into a psychological hole, it’s not worth forcing it just because “everyone bulks on Deca.”

Go slower, build quality tissue, and stay consistent. “Fast” isn’t always sustainable, but steady growth almost always wins long term.

Btw…
Bulking has way more to do with your training, diet, and total calorie surplus than the specific compounds you pick. Steroids amplify the signal your training and nutrition send — they don’t replace them. I’ve seen guys in pre-contest prep running NPP + Anadrol while getting lean because their diet dictated the outcome, not the drugs. If your diet and training are locked in, you’ll grow even on lower-risk compounds. Dial those in first, and then let the drugs assist the process instead of relying on them as the foundation. You got this. Good luck, brother man !

I had this exact same experience when first trying Deca all those years back, sure it takes around 5 weeks to peak in your bloodstream but that doesn't mean you will feel nothing until week 5 then suddenly you will get the side effects and anxiety. Like Test E, it begins building up as soon as you inject the stuff. I would find that I would inject the Deca, then 48 hours later I would get the anxiety really peak as the decanoate ester is cleaved off. Would also give me bad stomach ache too. But yes a very bad feeling of anxiety, nervousness and slight depression too. I wanted the size and strength gains so badly from it but the way it made me feel outweighed the potential positives. All was not lost though, I soon gave NPP a try and even though effectively they are both still Nandrolone - the feeling of Phenylpropionate ester attached to it gives a very different experience. NPP when you get a good version gives a great feeling of energy, positivity, strength, size and joint relief if you like to lift heavy. It also reads helps my appetite too alongside Test. Try it at 40 to 50mg per day or 100mg EOD and see how you find it. E.Q is another very bad choice if you get anxiety. Anadrol I find can make you feel quite like Deca does with that dark depressive nature. Bare in mind that carrier oils can influence a lot how a compound feels too, if you get a nice MCT it will make you feel mentally great and focused.

Honestly probably placebo cuz you read too much and are over informed. Sometimes it's better to know less and just do shit. Like lift heavy compound moves eat ALLOT test deca dbol or adrol or rotate. Then eq, then maybe some tren.
Don't turn something simple into rocket science.
In your post you were wondering allot of diff shit. Just slow down take breathe and enjoy the process more the pumps the feeling great workouts the progress.
Don't over complicate shit. You already have it figured out u said it yourself right in the post that's exactly what someone experienced will tell you. You have 5 guys under me saying it who know what they're taking about. Especially the last 2.
I used to do the same thing that's why i say this I'd drive myself crazy wondering if i should be doing this instead or add that,
Wish u the best on your journey.

Definitely going to agree with the others here that it was likely that it wasn't the deca at 10 days in and possibly the Test C increase. Anxiety does happen to us all though when we are fully loaded in cycle and fight or flight response is at a constant. I get mine with tren and clen and take propanolol to tone it down. However I do think NPP may be a good option as its half life is way shorter so you can dial it back if it gets too heavy. 19-nors arent for everyone and everyone's genetics are different so they respond to some better than other compounds...luckily you have other options. Sometimes a little goes along way learning what works for you. Good luck.

You don’t need deca or npp. It’s all preference. If deca is a shitty compounds for you, don’t use it! But you’re right, npp will enter and leave your system a lot quicker than deca, so not a bad idea to try it. With that being said, I really don’t think deca could’ve been causing that anxiety in 10 days, the ester is too long. Should take 4-6 weeks to reach peak levels. BUT, if you’re concerned about a compound giving you anxiety, short esters are for you!

I’m going take a shot and say it was from bumping your testosterone up. Deca is a very long ester, I’m talking very little in the way of anything happening for six weeks or so, probably a little joint relief. The real magic doesn’t start until twelve weeks or so, even more at 16-18. The stuff wasn’t really in your system yet.