What causes involuntary ejaculation when horse riding and is there any way it can be controlled or prevented with medication, etc? I thought it maybe related to the prostate and the pressure when riding causes it. It worries me both spiritually and physically too
No, there is no medication that can prevent ejaculation. Perhaps try a different saddle? Why kind of saddle do you use now? If you think it's related to your prostate then an english saddle probably causes more pressure. I'd try a western saddle where you can lean back and relax more. To my knowledge the western saddles are just more comfortable, period! Also, a tight-fitting underwear may keep your penis from vibrating as much.
The western saddle is much wider, so I imagine there is less pressure on your groin area.
And english saddle, obviously.
And a western saddle.
The differences are pretty striking actually. The seat of a western saddle is often padded, and encourages the rider to lean backwards, relaxing. English saddles encourage a more forward leaning, upright posture which places more pressure on the groin.