I will speak from personal experience here. I found that it was difficult to overcome porn addiction while having a problem with alcohol at the same time. It actually took me years to realize this because I was convinced they were separate and unrelated. However, I learned that they were related and making the recovery process more difficult than had I only struggled with one of them. So I gave this some serious thought and here is what I came up with.

1. Every time I would drink my inhibitions and judgment were lowered and I would more easily justify looking at porn instead of thinking more logically and staying strong.

2. Drinking also caused my neurotransmitter levels to be low. I actually got tested to see what my levels were and they were way low. So this in turn made me not only want to drink but look at porn to get a rush of dopamine and other neurotransmitters to feel normal or excited. Of course with proper diet, exercise, and allowing yourself to go through the withdrawal period, these neurotransmitter levels can return back to normal making it easier to abstain from porn.

3. Because I had developed a weakness for alcohol, anytime I would look at porn and then feel down afterward I would turn to alcohol to temporarily feel numb and forget about how bad the porn viewing made me feel. Of course this only made both problems worse.

I believe this effect could apply to any drug of choice. Its certainly not going to help you to overcome porn by turning to another substance.