The most commonly used AAS in medicine are testosterone and its various esters (but most commonly testosterone undecanoate , testosterone enanthate , testosterone cypionate , and testosterone propionate ),  nandrolone esters (most commonly nandrolone decanoate and nandrolone phenylpropionate ), stanozolol , and metandienone (methandrostenolone).  Others also available and used commonly but to a lesser extent include methyltestosterone , oxandrolone , mesterolone , and oxymetholone , as well as drostanolone propionate , metenolone (methylandrostenolone), and fluoxymesterone .  Dihydrotestosterone (DHT; androstanolone, stanolone) and its esters are also notable, although they are not widely used in medicine.  Boldenone undecylenate and trenbolone acetate are used in veterinary medicine . 
The disruption of blood flow to the penis vein is a major cause of weakness of penis during sexual intercourse. Although, there are other causes to the weakness in erection such as suffering from diabetes for a long period of time which must have damage the nerve system, cardiovascular disorder, prostate cancer operations, side effects of using hard drugs, multiple sclerosis, hormonal disorders, alcohol and drug abuse, emotional problems such as depression, anxiety, fear of guilt, low self-esteem ; and also old age plays importance rule in the development of weak erection in a man’s life, because weak erection occur so much in the age bracket of 40 – 65 years. This age group seems to live in total weakness of penis due to their past activity in their early age.
When first administering steroids, a man will have an increase in sexual function. This unfortunately is only temporary as your body becomes used to the steroid in its system. With prolonged use of a steroid, eventually, the man will feel less sexual desire, and will be less capable of maintaining an erection. Luckily, this is only temporary as well and can even be totally prevented with the use of substance such as Gonakor and HCG. Also when the steroid use is discontinued, the body’s natural level of testosterone (like the immune system) will certainly be suppressed.