### instruction:
If you are a doctor, please answer the medical questions based on the patient's description.

### input:
Hello. I am a 20 year old guy. I have been masturbating since the last 8 years. 1. I stroke it with my pants on(till just before I ejaculate)and in a lying position. Sometimes I get erect without even touching when I am in lying position. My erection goes softer when I open my pants and also goes away rapidly when I stand up, unless I keep stimulating it and doing it fast. Is doing it with pants on and while lying down a reason for this? I am concerned. To add, when I am with my girlfriend, even while making out generally over clothes, I get strong erections regardless of my posture. What is the cause of losing erection? I am extremely worried 2. I sometimes smoke marijuana. To be very honest, I do it in a very controlled way, like at a friendly get together or something. At MOST, I smoke it once or twice a week. Is this going to affect my sexual abilities in anyway in the long run? Does marijuana consumption have any effect on someones sexual factors? 3. What are the foods that I should have to last longer and have better erections? I have heard that some foods like bananna, onions and salmon increase the length of ones penis? Is that true? If it is, considering my age(20) if I consume those foods more, will I grow? I have made A huge post. Please PLEASE PLEASE, reply to each of my questions. It will be of great help. I would like to add that I am still new to some things. I am a virgin and I havent yet been involved in any kind of oral sex with my girlfriend. All I have done is made out over clothes.

### output:

Hi,1) Masturbation is not the cause for your problem. 2) Masturbating in a peculiar position (Lying position with pant) is not a disease condition, its individuals desire. (I had a patient he was 25 year when he came to my office for consultation he had a peculiar masturbatory position that is he can maintain the erection and ejaculate only rubbing over hard post like objects), Your masturbatory habit may be like this, you adapted this method for your masturbation. 3) To maintain erection all men require mental stimulation and physical stimulation. Position change and anxiety reduces erection, it is also common. Regular practice make you comfort in all position.4) Marijuana - Long term regular use definitely affect your sexual health. 5) Do regular exercise in open air, take green vegetables, avoid consumption of Alcohol and smoking. 6) An adult male require 4 c.m length (Full erect length) penis is enough to satisfy a female, if you have more than 4 c.m penis forget worry about size. 7) No specific foods to increases the size of penis, some foods will help to produce testosterone (Male sex hormones).