Yes, Androgen Deprivation Therapy (ADT) can cause penis shrinkage. By suppressing testosterone, the therapy leads to the structural atrophy of erectile tissue and reduced blood flow. While testicle and penis size reduction is an expected side effect, it often reverses once ADT is completed

Some more information your doctor may not have covered

Due to their different mechanisms of action. ADT which includes Orgovyx, Firmagon, Lupron, Eligard, Prostap, Camcevi, Lucrin, Zoladex, Trelstar, Pamorelin, and Decapeptyl can cause numerous side effects. Actually due to a lack of testosterone.
Hot flashes
Fatigue
Muscle deterioration
Bone weakening
Brain fog
Depression
Weight gain
Joint pain
Difficulty in breathing

Not all of these side effects occur to everyone on the drugs. Most of them are just things you have to be aware of and circumvent. I walk fast on a track twice a day, 1 mile at least, to help prevent bone weakening, fatigue and muscle deterioration. I also go to the gym three days a week (usually) and spend an hour with all different types of weight exercises. One thing that happens is people get a beer belly from the muscle deterioration, I do a lot of sit-ups to offset that.

Some people get depression but it is not common. It is easily treatable, according to people that have reported it on here and on Online Meetings I have participated in. If he has that problem Come back and ask for help, Or see a psychiatrist about doing something to relieve the depression.

Some people get no hot flashes at all. Others only have a few hot flashes and they are very minor. I had severe hot flashes for the first year on Lupron. As a hot flash was hitting I would feel a lot of fatigue. After a year, my oncologist prescribed a depo-provera shot every three months and it really stopped those hot flashes on Lupron. There are other hormones that can do this, speak to your doctor. If you have this problem, we can give you a list of drugs that can stop it. Ae doctor at a recent conference, put out a big list. I wear a Embrlabs.com Wave 2 device. It can reduce the hot flashes during the day and at night pretty much stops them completely. Megestrol has worked for some people.

I know one person that says eating tofu every day really controlled his hot flashes, another person in this forum said the same thing. Tofu does have properties similar to endocrine hormones but a lot weaker. Can’t hurt to try it. Seems they ate it daily.

According to a doctor that spoke to a recent webinar, many people on ADT, if they are staying on ADT for an extended period or have become castrate resistant should be taking bone straighteners. I took Fosamax for six years and I’m now on Zometa. That along with calcium taken daily helps keep your bones strong. Ask your doctor about this.

I have never gained any weight while on ADT. I get on the scale every morning and base what I eat on what I weigh. Skip lunch at times. Some people gain a lot of weight. The average is 5 pounds but some gain more and some gain none. Be aware that because you are on ADT you will find it very difficult to lose weight. That is one of the problems when you have a very little testosterone, you really have to work for it. Cutting out meals for weight loss often backfires by causing your metabolism to slow down and promoting fat storage as the body enters a survival-oriented "conservation mode". It leads to nutrient deficiencies, intense hunger causing overeating later, energy crashes, mental fatigue, and potential muscle loss.